[InstCombine] use nsw negation for abs libcalls

Also, produce the canonical IR abs (s<0) to be more efficient.

This is the libcall equivalent of the clang builtin change from:
rL333038

Pasting from that commit message:
The stdlib functions are defined in section 7.20.6.1 of the C standard with:
"If the result cannot be represented, the behavior is undefined."

That lets us mark the negation with 'nsw' because "sub i32 0, INT_MIN" would
be UB/poison.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333042 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/SimplifyLibCalls.cpp b/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 78864ea..32e47b6 100644 (file)
--- a/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1682,12 +1682,12 @@ Value *LibCallSimplifier::optimizeFls(CallInst *CI, IRBuilder<> &B) {
 }
 
 Value *LibCallSimplifier::optimizeAbs(CallInst *CI, IRBuilder<> &B) {
-  // abs(x) -> x >s -1 ? x : -x
-  Value *Op = CI->getArgOperand(0);
-  Value *Pos =
-      B.CreateICmpSGT(Op, Constant::getAllOnesValue(Op->getType()), "ispos");
-  Value *Neg = B.CreateNeg(Op, "neg");
-  return B.CreateSelect(Pos, Op, Neg);
+  // abs(x) -> x <s 0 ? -x : x
+  // The negation has 'nsw' because abs of INT_MIN is undefined.
+  Value *X = CI->getArgOperand(0);
+  Value *IsNeg = B.CreateICmpSLT(X, Constant::getNullValue(X->getType()));
+  Value *NegX = B.CreateNSWNeg(X, "neg");
+  return B.CreateSelect(IsNeg, NegX, X);
 }
 
 Value *LibCallSimplifier::optimizeIsDigit(CallInst *CI, IRBuilder<> &B) {
@@ -2716,4 +2716,4 @@ Value *FortifiedLibCallSimplifier::optimizeCall(CallInst *CI) {
 
 FortifiedLibCallSimplifier::FortifiedLibCallSimplifier(
     const TargetLibraryInfo *TLI, bool OnlyLowerUnknownSize)
-    : TLI(TLI), OnlyLowerUnknownSize(OnlyLowerUnknownSize) {}
\ No newline at end of file
+    : TLI(TLI), OnlyLowerUnknownSize(OnlyLowerUnknownSize) {}

diff --git a/test/Transforms/InstCombine/abs-1.ll b/test/Transforms/InstCombine/abs-1.ll
index 85543f9..ab1813c 100644 (file)
--- a/test/Transforms/InstCombine/abs-1.ll
+++ b/test/Transforms/InstCombine/abs-1.ll
@@ -12,10 +12,10 @@ declare i64 @llabs(i64)
 
 define i32 @test_abs(i32 %x) {
 ; CHECK-LABEL: @test_abs(
-; CHECK-NEXT:    [[ISPOS:%.*]] = icmp slt i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[NEG:%.*]] = sub i32 0, [[X]]
-; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[ISPOS]], i32 [[NEG]], i32 [[X]]
-; CHECK-NEXT:    ret i32 [[TMP1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i32 [[X:%.*]], 0
+; CHECK-NEXT:    [[NEG:%.*]] = sub nsw i32 0, [[X]]
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i32 [[NEG]], i32 [[X]]
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
   %ret = call i32 @abs(i32 %x)
   ret i32 %ret
@@ -23,10 +23,10 @@ define i32 @test_abs(i32 %x) {
 
 define i64 @test_labs(i64 %x) {
 ; CHECK-LABEL: @test_labs(
-; CHECK-NEXT:    [[ISPOS:%.*]] = icmp slt i64 [[X:%.*]], 0
-; CHECK-NEXT:    [[NEG:%.*]] = sub i64 0, [[X]]
-; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[ISPOS]], i64 [[NEG]], i64 [[X]]
-; CHECK-NEXT:    ret i64 [[TMP1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i64 [[X:%.*]], 0
+; CHECK-NEXT:    [[NEG:%.*]] = sub nsw i64 0, [[X]]
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[NEG]], i64 [[X]]
+; CHECK-NEXT:    ret i64 [[TMP2]]
 ;
   %ret = call i64 @labs(i64 %x)
   ret i64 %ret
@@ -34,10 +34,10 @@ define i64 @test_labs(i64 %x) {
 
 define i64 @test_llabs(i64 %x) {
 ; CHECK-LABEL: @test_llabs(
-; CHECK-NEXT:    [[ISPOS:%.*]] = icmp slt i64 [[X:%.*]], 0
-; CHECK-NEXT:    [[NEG:%.*]] = sub i64 0, [[X]]
-; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[ISPOS]], i64 [[NEG]], i64 [[X]]
-; CHECK-NEXT:    ret i64 [[TMP1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i64 [[X:%.*]], 0
+; CHECK-NEXT:    [[NEG:%.*]] = sub nsw i64 0, [[X]]
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[NEG]], i64 [[X]]
+; CHECK-NEXT:    ret i64 [[TMP2]]
 ;
   %ret = call i64 @llabs(i64 %x)
   ret i64 %ret

diff --git a/test/Transforms/InstCombine/call-callconv.ll b/test/Transforms/InstCombine/call-callconv.ll
index f7f0d3a..0cb2c55 100644 (file)
--- a/test/Transforms/InstCombine/call-callconv.ll
+++ b/test/Transforms/InstCombine/call-callconv.ll
@@ -6,10 +6,10 @@
 
 define arm_aapcscc i32 @_abs(i32 %i) nounwind readnone {
 ; CHECK-LABEL: @_abs(
-; CHECK-NEXT:    [[ISPOS:%.*]] = icmp slt i32 [[I:%.*]], 0
-; CHECK-NEXT:    [[NEG:%.*]] = sub i32 0, [[I]]
-; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[ISPOS]], i32 [[NEG]], i32 [[I]]
-; CHECK-NEXT:    ret i32 [[TMP1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i32 [[I:%.*]], 0
+; CHECK-NEXT:    [[NEG:%.*]] = sub nsw i32 0, [[I]]
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i32 [[NEG]], i32 [[I]]
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
   %call = tail call arm_aapcscc i32 @abs(i32 %i) nounwind readnone
   ret i32 %call
@@ -19,10 +19,10 @@ declare arm_aapcscc i32 @abs(i32) nounwind readnone
 
 define arm_aapcscc i32 @_labs(i32 %i) nounwind readnone {
 ; CHECK-LABEL: @_labs(
-; CHECK-NEXT:    [[ISPOS:%.*]] = icmp slt i32 [[I:%.*]], 0
-; CHECK-NEXT:    [[NEG:%.*]] = sub i32 0, [[I]]
-; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[ISPOS]], i32 [[NEG]], i32 [[I]]
-; CHECK-NEXT:    ret i32 [[TMP1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i32 [[I:%.*]], 0
+; CHECK-NEXT:    [[NEG:%.*]] = sub nsw i32 0, [[I]]
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i32 [[NEG]], i32 [[I]]
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
   %call = tail call arm_aapcscc i32 @labs(i32 %i) nounwind readnone
   ret i32 %call