gnu: llvm-9: Backport patch to fix miscompilation for big-endian targets.

* gnu/packages/llvm.scm (llvm-9)[source]: Add new patch. * gnu/packages/patches/llvm-9-fix-bitcast-miscompilation.patch: New file. * gnu/local.mk (dist_patch_DATA): Register new file.
2 years ago · ff2f86114c
3 changed files with 194 additions and 0 deletions
--- a/gnu/local.mk
+++ b/gnu/local.mk
@ -1242,6 +1242,7 @@ dist_patch_DATA =						\
  %D%/packages/patches/lirc-localstatedir.patch			\
  %D%/packages/patches/lirc-reproducible-build.patch		\
  %D%/packages/patches/llvm-3.5-fix-clang-build-with-gcc5.patch	\
+  %D%/packages/patches/llvm-9-fix-bitcast-miscompilation.patch	\
  %D%/packages/patches/llvm-9-fix-lpad-miscompilation.patch	\
  %D%/packages/patches/llvm-9-fix-scev-miscompilation.patch	\
  %D%/packages/patches/lm-sensors-hwmon-attrs.patch		\
--- a/gnu/packages/llvm.scm
+++ b/gnu/packages/llvm.scm
@ -514,6 +514,7 @@ output), and Binutils.")
         "16hwp3qa54c3a3v7h8nlw0fh5criqh0hlr1skybyk0cz70gyx880"))
       (patch-flags '("-p2"))
       (patches (search-patches
+                  "llvm-9-fix-bitcast-miscompilation.patch"
                  "llvm-9-fix-scev-miscompilation.patch"
                  "llvm-9-fix-lpad-miscompilation.patch"))))))

--- a/gnu/packages/patches/llvm-9-fix-bitcast-miscompilation.patch
+++ b/gnu/packages/patches/llvm-9-fix-bitcast-miscompilation.patch
@ -0,0 +1,192 @@
+From f8e146f3430de3a6cd904f3f3f7aa1bfaefee14c Mon Sep 17 00:00:00 2001
+From: Bjorn Pettersson <bjorn.a.pettersson@ericsson.com>
+Date: Thu, 28 Nov 2019 23:18:28 +0100
+Subject: [PATCH] [InstCombine] Fix big-endian miscompile of (bitcast
+ (zext/trunc (bitcast)))
+
+Summary:
+optimizeVectorResize is rewriting patterns like:
+  %1 = bitcast vector %src to integer
+  %2 = trunc/zext %1
+  %dst = bitcast %2 to vector
+
+Since bitcasting between integer an vector types gives
+different integer values depending on endianness, we need
+to take endianness into account. As it happens the old
+implementation only produced the correct result for little
+endian targets.
+
+Fixes: https://bugs.llvm.org/show_bug.cgi?id=44178
+
+Reviewers: spatel, lattner, lebedev.ri
+
+Reviewed By: spatel, lebedev.ri
+
+Subscribers: lebedev.ri, hiraditya, uabelho, llvm-commits
+
+Tags: #llvm
+
+Differential Revision: https://reviews.llvm.org/D70844
+
+(cherry picked from commit a9d6b0e5444741d08ff1df7cf71d1559e7fefc1f)
+---
+ .../InstCombine/InstCombineCasts.cpp          | 79 +++++++++++++------
+ llvm/test/Transforms/InstCombine/cast.ll      |  6 +-
+ 2 files changed, 60 insertions(+), 25 deletions(-)
+
+diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+index 2c9ba203fbf3..0af3de300e77 100644
+--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+@@ -18,6 +18,7 @@
+ #include "llvm/IR/DIBuilder.h"
+ #include "llvm/IR/PatternMatch.h"
+ #include "llvm/Support/KnownBits.h"
+#include <numeric>
+ using namespace llvm;
+ using namespace PatternMatch;
+ 
+@@ -1820,12 +1821,24 @@ Instruction *InstCombiner::visitPtrToInt(PtrToIntInst &CI) {
+ }
+ 
+ /// This input value (which is known to have vector type) is being zero extended
+-/// or truncated to the specified vector type.
+/// or truncated to the specified vector type. Since the zext/trunc is done
+/// using an integer type, we have a (bitcast(cast(bitcast))) pattern,
+/// endianness will impact which end of the vector that is extended or
+/// truncated.
+///
+/// A vector is always stored with index 0 at the lowest address, which
+/// corresponds to the most significant bits for a big endian stored integer and
+/// the least significant bits for little endian. A trunc/zext of an integer
+/// impacts the big end of the integer. Thus, we need to add/remove elements at
+/// the front of the vector for big endian targets, and the back of the vector
+/// for little endian targets.
+///
+ /// Try to replace it with a shuffle (and vector/vector bitcast) if possible.
+ ///
+ /// The source and destination vector types may have different element types.
+-static Instruction *optimizeVectorResize(Value *InVal, VectorType *DestTy,
+-                                         InstCombiner &IC) {
+static Instruction *optimizeVectorResizeWithIntegerBitCasts(Value *InVal,
+                                                            VectorType *DestTy,
+                                                            InstCombiner &IC) {
+   // We can only do this optimization if the output is a multiple of the input
+   // element size, or the input is a multiple of the output element size.
+   // Convert the input type to have the same element type as the output.
+@@ -1844,31 +1857,53 @@ static Instruction *optimizeVectorResize(Value *InVal, VectorType *DestTy,
+     InVal = IC.Builder.CreateBitCast(InVal, SrcTy);
+   }
+ 
+  bool IsBigEndian = IC.getDataLayout().isBigEndian();
+  unsigned SrcElts = SrcTy->getNumElements();
+  unsigned DestElts = DestTy->getNumElements();
+
+  assert(SrcElts != DestElts && "Element counts should be different.");
+
+   // Now that the element types match, get the shuffle mask and RHS of the
+   // shuffle to use, which depends on whether we're increasing or decreasing the
+   // size of the input.
+-  SmallVector<uint32_t, 16> ShuffleMask;
+  SmallVector<uint32_t, 16> ShuffleMaskStorage;
+  ArrayRef<uint32_t> ShuffleMask;
+   Value *V2;
+ 
+-  if (SrcTy->getNumElements() > DestTy->getNumElements()) {
+-    // If we're shrinking the number of elements, just shuffle in the low
+-    // elements from the input and use undef as the second shuffle input.
+-    V2 = UndefValue::get(SrcTy);
+-    for (unsigned i = 0, e = DestTy->getNumElements(); i != e; ++i)
+-      ShuffleMask.push_back(i);
+  // Produce an identify shuffle mask for the src vector.
+  ShuffleMaskStorage.resize(SrcElts);
+  std::iota(ShuffleMaskStorage.begin(), ShuffleMaskStorage.end(), 0);
+ 
+  if (SrcElts > DestElts) {
+    // If we're shrinking the number of elements (rewriting an integer
+    // truncate), just shuffle in the elements corresponding to the least
+    // significant bits from the input and use undef as the second shuffle
+    // input.
+    V2 = UndefValue::get(SrcTy);
+    // Make sure the shuffle mask selects the "least significant bits" by
+    // keeping elements from back of the src vector for big endian, and from the
+    // front for little endian.
+    ShuffleMask = ShuffleMaskStorage;
+    if (IsBigEndian)
+      ShuffleMask = ShuffleMask.take_back(DestElts);
+    else
+      ShuffleMask = ShuffleMask.take_front(DestElts);
+   } else {
+-    // If we're increasing the number of elements, shuffle in all of the
+-    // elements from InVal and fill the rest of the result elements with zeros
+-    // from a constant zero.
+    // If we're increasing the number of elements (rewriting an integer zext),
+    // shuffle in all of the elements from InVal. Fill the rest of the result
+    // elements with zeros from a constant zero.
+     V2 = Constant::getNullValue(SrcTy);
+-    unsigned SrcElts = SrcTy->getNumElements();
+-    for (unsigned i = 0, e = SrcElts; i != e; ++i)
+-      ShuffleMask.push_back(i);
+-
+-    // The excess elements reference the first element of the zero input.
+-    for (unsigned i = 0, e = DestTy->getNumElements()-SrcElts; i != e; ++i)
+-      ShuffleMask.push_back(SrcElts);
+    // Use first elt from V2 when indicating zero in the shuffle mask.
+    uint32_t NullElt = SrcElts;
+    // Extend with null values in the "most significant bits" by adding elements
+    // in front of the src vector for big endian, and at the back for little
+    // endian.
+    unsigned DeltaElts = DestElts - SrcElts;
+    if (IsBigEndian)
+      ShuffleMaskStorage.insert(ShuffleMaskStorage.begin(), DeltaElts, NullElt);
+    else
+      ShuffleMaskStorage.append(DeltaElts, NullElt);
+    ShuffleMask = ShuffleMaskStorage;
+   }
+ 
+   return new ShuffleVectorInst(InVal, V2,
+@@ -2359,8 +2394,8 @@ Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
+         CastInst *SrcCast = cast<CastInst>(Src);
+         if (BitCastInst *BCIn = dyn_cast<BitCastInst>(SrcCast->getOperand(0)))
+           if (isa<VectorType>(BCIn->getOperand(0)->getType()))
+-            if (Instruction *I = optimizeVectorResize(BCIn->getOperand(0),
+-                                               cast<VectorType>(DestTy), *this))
+            if (Instruction *I = optimizeVectorResizeWithIntegerBitCasts(
+                    BCIn->getOperand(0), cast<VectorType>(DestTy), *this))
+               return I;
+       }
+ 
+diff --git a/llvm/test/Transforms/InstCombine/cast.ll b/llvm/test/Transforms/InstCombine/cast.ll
+index b6d1eda0601d..3ce8de033422 100644
+--- a/llvm/test/Transforms/InstCombine/cast.ll
+++ b/llvm/test/Transforms/InstCombine/cast.ll
+@@ -824,7 +824,7 @@ define i64 @test59(i8 %A, i8 %B) {
+ 
+ define <3 x i32> @test60(<4 x i32> %call4) {
+ ; CHECK-LABEL: @test60(
+-; CHECK-NEXT:    [[P10:%.*]] = shufflevector <4 x i32> [[CALL4:%.*]], <4 x i32> undef, <3 x i32> <i32 0, i32 1, i32 2>
+; CHECK-NEXT:    [[P10:%.*]] = shufflevector <4 x i32> [[CALL4:%.*]], <4 x i32> undef, <3 x i32> <i32 1, i32 2, i32 3>
+ ; CHECK-NEXT:    ret <3 x i32> [[P10]]
+ ;
+   %p11 = bitcast <4 x i32> %call4 to i128
+@@ -836,7 +836,7 @@ define <3 x i32> @test60(<4 x i32> %call4) {
+ 
+ define <4 x i32> @test61(<3 x i32> %call4) {
+ ; CHECK-LABEL: @test61(
+-; CHECK-NEXT:    [[P10:%.*]] = shufflevector <3 x i32> [[CALL4:%.*]], <3 x i32> <i32 0, i32 undef, i32 undef>, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    [[P10:%.*]] = shufflevector <3 x i32> [[CALL4:%.*]], <3 x i32> <i32 0, i32 undef, i32 undef>, <4 x i32> <i32 3, i32 0, i32 1, i32 2>
+ ; CHECK-NEXT:    ret <4 x i32> [[P10]]
+ ;
+   %p11 = bitcast <3 x i32> %call4 to i96
+@@ -848,7 +848,7 @@ define <4 x i32> @test61(<3 x i32> %call4) {
+ define <4 x i32> @test62(<3 x float> %call4) {
+ ; CHECK-LABEL: @test62(
+ ; CHECK-NEXT:    [[TMP1:%.*]] = bitcast <3 x float> [[CALL4:%.*]] to <3 x i32>
+-; CHECK-NEXT:    [[P10:%.*]] = shufflevector <3 x i32> [[TMP1]], <3 x i32> <i32 0, i32 undef, i32 undef>, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    [[P10:%.*]] = shufflevector <3 x i32> [[TMP1]], <3 x i32> <i32 0, i32 undef, i32 undef>, <4 x i32> <i32 3, i32 0, i32 1, i32 2>
+ ; CHECK-NEXT:    ret <4 x i32> [[P10]]
+ ;
+   %p11 = bitcast <3 x float> %call4 to i96
+-- 
+2.26.2
+