InstCombine: mul to shl shouldn't preserve nsw

consider:
mul i32 nsw %x, -2147483648

this instruction will not result in poison if %x is 1

however, if we transform this into:
shl i32 nsw %x, 31

then we will be generating poison because we just shifted into the sign
bit.

This fixes PR21242.

llvm-svn: 219566

llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

@@ -176,8 +176,6 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
       if (NewCst) {
         BinaryOperator *Shl = BinaryOperator::CreateShl(NewOp, NewCst);
 
-        if (I.hasNoSignedWrap())
-          Shl->setHasNoSignedWrap();
         if (I.hasNoUnsignedWrap())
           Shl->setHasNoUnsignedWrap();
 

llvm/test/Transforms/InstCombine/2011-06-13-nsw-alloca.ll

@@ -15,7 +15,7 @@ define void @fu1(i32 %parm) nounwind ssp {
 
 ; <label>:4                                       ; preds = %0
   %5 = load i32* %1, align 4
-  %6 = mul nsw i32 %5, 8
+  %6 = shl nsw i32 %5, 3
 ; With "nsw", the alloca and its bitcast can be fused:
   %7 = add nsw i32 %6, 2048
 ;  CHECK: alloca double

llvm/test/Transforms/InstCombine/add2.ll

@@ -219,7 +219,7 @@ define i16 @mul_add_to_mul_1(i16 %x) {
  %add2 = add nsw i16 %x, %mul1
  ret i16 %add2
 ; CHECK-LABEL: @mul_add_to_mul_1(
-; CHECK-NEXT: %add2 = mul nsw i16 %x, 9
+; CHECK-NEXT: %add2 = mul i16 %x, 9
 ; CHECK-NEXT: ret i16 %add2
 }
 
@@ -228,7 +228,7 @@ define i16 @mul_add_to_mul_2(i16 %x) {
  %add2 = add nsw i16 %mul1, %x
  ret i16 %add2
 ; CHECK-LABEL: @mul_add_to_mul_2(
-; CHECK-NEXT: %add2 = mul nsw i16 %x, 9
+; CHECK-NEXT: %add2 = mul i16 %x, 9
 ; CHECK-NEXT: ret i16 %add2
 }
 
@@ -248,7 +248,7 @@ define i16 @mul_add_to_mul_4(i16 %a) {
  %add = add nsw i16 %mul1, %mul2
  ret i16 %add
 ; CHECK-LABEL: @mul_add_to_mul_4(
-; CHECK-NEXT: %add = mul nsw i16 %a, 9
+; CHECK-NEXT: %add = mul i16 %a, 9
 ; CHECK-NEXT: ret i16 %add
 }
 

llvm/test/Transforms/InstCombine/cast.ll

@@ -810,7 +810,7 @@ define double @test71(double *%p, i64 %i) {
 
 define double @test72(double *%p, i32 %i) {
 ; CHECK-LABEL: @test72(
-  %so = mul nsw i32 %i, 8
+  %so = shl nsw i32 %i, 3
   %o = sext i32 %so to i64
 ; CHECK-NEXT: sext i32 %i to i64
   %q = bitcast double* %p to i8*
@@ -825,7 +825,7 @@ define double @test72(double *%p, i32 %i) {
 
 define double @test73(double *%p, i128 %i) {
 ; CHECK-LABEL: @test73(
-  %lo = mul nsw i128 %i, 8
+  %lo = shl nsw i128 %i, 3
   %o = trunc i128 %lo to i64
 ; CHECK-NEXT: trunc i128 %i to i64
   %q = bitcast double* %p to i8*
@@ -937,7 +937,7 @@ define %s @test79(%s *%p, i64 %i, i32 %j) {
 
 define double @test80([100 x double]* %p, i32 %i) {
 ; CHECK-LABEL: @test80(
-  %tmp = mul nsw i32 %i, 8
+  %tmp = shl nsw i32 %i, 3
 ; CHECK-NEXT: sext i32 %i to i64
   %q = bitcast [100 x double]* %p to i8*
   %pp = getelementptr i8* %q, i32 %tmp
@@ -954,7 +954,7 @@ define double @test80_addrspacecast([100 x double] addrspace(1)* %p, i32 %i) {
 ; CHECK-NEXT: getelementptr [100 x double] addrspace(1)* %p
 ; CHECK-NEXT: load double addrspace(1)*
 ; CHECK-NEXT: ret double
-  %tmp = mul nsw i32 %i, 8
+  %tmp = shl nsw i32 %i, 3
   %q = addrspacecast [100 x double] addrspace(1)* %p to i8 addrspace(2)*
   %pp = getelementptr i8 addrspace(2)* %q, i32 %tmp
   %r = addrspacecast i8 addrspace(2)* %pp to double addrspace(1)*
@@ -968,7 +968,7 @@ define double @test80_addrspacecast_2([100 x double] addrspace(1)* %p, i32 %i) {
 ; CHECK-NEXT: addrspacecast double addrspace(1)*
 ; CHECK-NEXT: load double addrspace(3)*
 ; CHECK-NEXT: ret double
-  %tmp = mul nsw i32 %i, 8
+  %tmp = shl nsw i32 %i, 3
   %q = addrspacecast [100 x double] addrspace(1)* %p to i8 addrspace(2)*
   %pp = getelementptr i8 addrspace(2)* %q, i32 %tmp
   %r = addrspacecast i8 addrspace(2)* %pp to double addrspace(3)*
@@ -978,7 +978,7 @@ define double @test80_addrspacecast_2([100 x double] addrspace(1)* %p, i32 %i) {
 
 define double @test80_as1([100 x double] addrspace(1)* %p, i16 %i) {
 ; CHECK-LABEL: @test80_as1(
-  %tmp = mul nsw i16 %i, 8
+  %tmp = shl nsw i16 %i, 3
 ; CHECK-NEXT: sext i16 %i to i32
   %q = bitcast [100 x double] addrspace(1)* %p to i8 addrspace(1)*
   %pp = getelementptr i8 addrspace(1)* %q, i16 %tmp

llvm/test/Transforms/InstCombine/div.ll

@@ -217,7 +217,7 @@ define i32 @test25(i32 %a) {
   %div = sdiv i32 %shl, 2
   ret i32 %div
 ; CHECK-LABEL: @test25(
-; CHECK-NEXT: %div = shl nsw i32 %a, 1
+; CHECK-NEXT: %div = shl i32 %a, 1
 ; CHECK-NEXT: ret i32 %div
 }
 
@@ -226,7 +226,7 @@ define i32 @test26(i32 %a) {
   %div = sdiv i32 %mul, 3
   ret i32 %div
 ; CHECK-LABEL: @test26(
-; CHECK-NEXT: %div = shl nsw i32 %a, 2
+; CHECK-NEXT: %div = shl i32 %a, 2
 ; CHECK-NEXT: ret i32 %div
 }