From: Sanjay Patel <spatel@rotateright.com>
Date: Wed, 9 Jul 2014 16:34:54 +0000 (+0000)
Subject: Fix for PR20059 (instcombine reorders shufflevector after instruction that may trap)
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=296cb7b128114eda207f96c65513335efe46a1d5;p=oota-llvm.git

Fix for PR20059 (instcombine reorders shufflevector after instruction that may trap)

In PR20059 ( http://llvm.org/pr20059 ), instcombine eliminates shuffles that are necessary before performing an operation that can trap (srem).

This patch calls isSafeToSpeculativelyExecute() and bails out of the optimization in SimplifyVectorOp() if needed.

Differential Revision: http://reviews.llvm.org/D4424



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212629 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index 6cba8e37509..487699c41e9 100644
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -42,6 +42,7 @@
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/GetElementPtrTypeIterator.h"
@@ -1195,6 +1196,11 @@ static Value *CreateBinOpAsGiven(BinaryOperator &Inst, Value *LHS, Value *RHS,
 Value *InstCombiner::SimplifyVectorOp(BinaryOperator &Inst) {
   if (!Inst.getType()->isVectorTy()) return nullptr;
 
+  // It may not be safe to reorder shuffles and things like div, urem, etc.
+  // because we may trap when executing those ops on unknown vector elements.
+  // See PR20059.
+  if (!isSafeToSpeculativelyExecute(&Inst)) return nullptr;
+
   unsigned VWidth = cast<VectorType>(Inst.getType())->getNumElements();
   Value *LHS = Inst.getOperand(0), *RHS = Inst.getOperand(1);
   assert(cast<VectorType>(LHS->getType())->getNumElements() == VWidth);
diff --git a/test/Transforms/InstCombine/pr20059.ll b/test/Transforms/InstCombine/pr20059.ll
new file mode 100644
index 00000000000..8d7d69bf876
--- /dev/null
+++ b/test/Transforms/InstCombine/pr20059.ll
@@ -0,0 +1,32 @@
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+; In PR20059 ( http://llvm.org/pr20059 ), shufflevector operations are reordered/removed
+; for an srem operation. This is not a valid optimization because it may cause a trap
+; on div-by-zero.
+
+; CHECK-LABEL: @do_not_reorder
+; CHECK: %splat1 = shufflevector <4 x i32> %p1, <4 x i32> undef, <4 x i32> zeroinitializer
+; CHECK-NEXT: %splat2 = shufflevector <4 x i32> %p2, <4 x i32> undef, <4 x i32> zeroinitializer
+; CHECK-NEXT: %retval = srem <4 x i32> %splat1, %splat2
+define <4 x i32> @do_not_reorder(<4 x i32> %p1, <4 x i32> %p2) {
+  %splat1 = shufflevector <4 x i32> %p1, <4 x i32> undef, <4 x i32> zeroinitializer
+  %splat2 = shufflevector <4 x i32> %p2, <4 x i32> undef, <4 x i32> zeroinitializer
+  %retval = srem <4 x i32> %splat1, %splat2
+  ret <4 x i32> %retval
+}
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+; In PR20059 ( http://llvm.org/pr20059 ), shufflevector operations are reordered/removed
+; for an srem operation. This is not a valid optimization because it may cause a trap
+; on div-by-zero.
+
+; CHECK-LABEL: @do_not_reorder
+; CHECK: %splat1 = shufflevector <4 x i32> %p1, <4 x i32> undef, <4 x i32> zeroinitializer
+; CHECK-NEXT: %splat2 = shufflevector <4 x i32> %p2, <4 x i32> undef, <4 x i32> zeroinitializer
+; CHECK-NEXT: %retval = srem <4 x i32> %splat1, %splat2
+define <4 x i32> @do_not_reorder(<4 x i32> %p1, <4 x i32> %p2) {
+  %splat1 = shufflevector <4 x i32> %p1, <4 x i32> undef, <4 x i32> zeroinitializer
+  %splat2 = shufflevector <4 x i32> %p2, <4 x i32> undef, <4 x i32> zeroinitializer
+  %retval = srem <4 x i32> %splat1, %splat2
+  ret <4 x i32> %retval
+}