From 70635adea36679b98bbc87f196548ed42a244a29 Mon Sep 17 00:00:00 2001
From: Bill Wendling <isanbard@gmail.com>
Date: Sun, 30 Nov 2008 03:42:12 +0000
Subject: [PATCH] Instcombine was illegally transforming -X/C into X/-C when
 either X or C overflowed on negation. This commit checks to make sure that
 neithe C nor X overflows. This requires that the RHS of X (a subtract
 instruction) be a constant integer.

llvm-svn: 60275
---
 .../Scalar/InstructionCombining.cpp           | 23 ++++++++++++++++---
 llvm/test/Transforms/InstCombine/apint-sub.ll |  8 ++++---
 llvm/test/Transforms/InstCombine/sdiv-1.ll    | 22 ++++++++++++++++++
 llvm/test/Transforms/InstCombine/sub.ll       |  8 ++++---
 4 files changed, 52 insertions(+), 9 deletions(-)
 create mode 100644 llvm/test/Transforms/InstCombine/sdiv-1.ll

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 9214b6bbd115..8461aa75e028 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -2956,9 +2956,26 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
     if (RHS->isAllOnesValue())
       return BinaryOperator::CreateNeg(Op0);
 
-    // -X/C -> X/-C
-    if (Value *LHSNeg = dyn_castNegVal(Op0))
-      return BinaryOperator::CreateSDiv(LHSNeg, ConstantExpr::getNeg(RHS));
+    ConstantInt *RHSNeg = cast<ConstantInt>(ConstantExpr::getNeg(RHS));
+
+    // -X/C -> X/-C, if and only if negation doesn't overflow.
+    if ((RHS->getSExtValue() < 0 &&
+         RHS->getSExtValue() < RHSNeg->getSExtValue()) ||
+        (RHS->getSExtValue() > 0 &&
+         RHS->getSExtValue() > RHSNeg->getSExtValue())) {
+      if (Value *LHSNeg = dyn_castNegVal(Op0)) {
+        if (ConstantInt *CI = dyn_cast<ConstantInt>(LHSNeg)) {
+          ConstantInt *CINeg = cast<ConstantInt>(ConstantExpr::getNeg(CI));
+
+          if ((CI->getSExtValue() < 0 &&
+               CI->getSExtValue() < CINeg->getSExtValue()) ||
+              (CI->getSExtValue() > 0 &&
+               CI->getSExtValue() > CINeg->getSExtValue()))
+            return BinaryOperator::CreateSDiv(LHSNeg,
+                                              ConstantExpr::getNeg(RHS));
+        }
+      }
+    }
   }
 
   // If the sign bits of both operands are zero (i.e. we can prove they are
diff --git a/llvm/test/Transforms/InstCombine/apint-sub.ll b/llvm/test/Transforms/InstCombine/apint-sub.ll
index 12f366de7f46..2ff763c9f5f8 100644
--- a/llvm/test/Transforms/InstCombine/apint-sub.ll
+++ b/llvm/test/Transforms/InstCombine/apint-sub.ll
@@ -3,7 +3,7 @@
 ;
 
 ; RUN: llvm-as < %s | opt -instcombine | llvm-dis | \
-; RUN:   grep -v {sub i19 %Cok, %Bok} | not grep sub
+; RUN:   grep -v {sub i19 %Cok, %Bok} | grep -v {sub i25 0, %Aok} | not grep sub
 ; END.
 
 define i23 @test1(i23 %A) {
@@ -107,8 +107,10 @@ define i51 @test16(i51 %A) {
 	ret i51 %Y
 }
 
-define i25 @test17(i25 %A) {
-	%B = sub i25 0, %A		; <i25> [#uses=1]
+; Can't fold subtract here because negation it might oveflow.
+; PR3142
+define i25 @test17(i25 %Aok) {
+	%B = sub i25 0, %Aok		; <i25> [#uses=1]
 	%C = sdiv i25 %B, 1234		; <i25> [#uses=1]
 	ret i25 %C
 }
diff --git a/llvm/test/Transforms/InstCombine/sdiv-1.ll b/llvm/test/Transforms/InstCombine/sdiv-1.ll
new file mode 100644
index 000000000000..c10bd775157a
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/sdiv-1.ll
@@ -0,0 +1,22 @@
+; RUN: llvm-as < %s | opt -instcombine -inline | llvm-dis | grep {715827882} | count 2
+; PR3142
+
+define i32 @a(i32 %X) nounwind readnone {
+entry:
+       %0 = sub i32 0, %X
+       %1 = sdiv i32 %0, -3
+       ret i32 %1
+}
+
+define i32 @b(i32 %X) nounwind readnone {
+entry:
+       %0 = call i32 @a(i32 -2147483648)
+       ret i32 %0
+}
+
+define i32 @c(i32 %X) nounwind readnone {
+entry:
+       %0 = sub i32 0, -2147483648
+       %1 = sdiv i32 %0, -3
+       ret i32 %1
+}
diff --git a/llvm/test/Transforms/InstCombine/sub.ll b/llvm/test/Transforms/InstCombine/sub.ll
index da6d710f6bc2..1ab4eaf1b49d 100644
--- a/llvm/test/Transforms/InstCombine/sub.ll
+++ b/llvm/test/Transforms/InstCombine/sub.ll
@@ -1,7 +1,7 @@
 ; This test makes sure that these instructions are properly eliminated.
 ;
 ; RUN: llvm-as < %s | opt -instcombine | llvm-dis | \
-; RUN:   grep -v {sub i32 %Cok, %Bok} | not grep sub
+; RUN:   grep -v {sub i32 %Cok, %Bok} | grep -v {sub i32 0, %Aok} | not grep sub
 
 define i32 @test1(i32 %A) {
 	%B = sub i32 %A, %A		; <i32> [#uses=1]
@@ -104,8 +104,10 @@ define i32 @test16(i32 %A) {
 	ret i32 %Y
 }
 
-define i32 @test17(i32 %A) {
-	%B = sub i32 0, %A		; <i32> [#uses=1]
+; Can't fold subtract here because negation it might oveflow.
+; PR3142
+define i32 @test17(i32 %Aok) {
+	%B = sub i32 0, %Aok		; <i32> [#uses=1]
 	%C = sdiv i32 %B, 1234		; <i32> [#uses=1]
 	ret i32 %C
 }
-- 
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