Revert remaining part of r93200: "Disable folding sext(trunc(x)) -> x"

This fixes PR5997.

These transforms were disabled because codegen couldn't deal with other
uses of trunc(x). This is now handled by the peephole pass.

This causes no regressions on x86-64.

llvm-svn: 159003

2 files changed, 11 insertions, 15 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index fa24800717e..555b4428d2e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -648,10 +648,8 @@ static bool CanEvaluateZExtd(Value *V, Type *Ty, unsigned &BitsToClear) {
   if (!I) return false;
   
   // If the input is a truncate from the destination type, we can trivially
-  // eliminate it, even if it has multiple uses.
-  // FIXME: This is currently disabled until codegen can handle this without
-  // pessimizing code, PR5997.
-  if (0 && isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
+  // eliminate it.
+  if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
     return true;
   
   // We can't extend or shrink something that has multiple uses: doing so would
@@ -992,11 +990,8 @@ static bool CanEvaluateSExtd(Value *V, Type *Ty) {
   Instruction *I = dyn_cast<Instruction>(V);
   if (!I) return false;
   
-  // If this is a truncate from the dest type, we can trivially eliminate it,
-  // even if it has multiple uses.
-  // FIXME: This is currently disabled until codegen can handle this without
-  // pessimizing code, PR5997.
-  if (0 && isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
+  // If this is a truncate from the dest type, we can trivially eliminate it.
+  if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
     return true;
   
   // We can't extend or shrink something that has multiple uses: doing so would
diff --git a/llvm/test/Transforms/InstCombine/trunc.ll b/llvm/test/Transforms/InstCombine/trunc.ll
index 6ec342a4f5c..cbbad7f7977 100644
--- a/llvm/test/Transforms/InstCombine/trunc.ll
+++ b/llvm/test/Transforms/InstCombine/trunc.ll
@@ -12,8 +12,8 @@ define i64 @test1(i64 %a) {
   call void @use(i32 %b)
   ret i64 %d
 ; CHECK: @test1
-; CHECK: %d = and i64 %a, 15
-; CHECK: ret i64 %d
+; CHECK-NOT: ext
+; CHECK: ret
 }
 define i64 @test2(i64 %a) {
   %b = trunc i64 %a to i32
@@ -34,8 +34,8 @@ define i64 @test3(i64 %a) {
   call void @use(i32 %b)
   ret i64 %d
 ; CHECK: @test3
-; CHECK: %d = and i64 %a, 8
-; CHECK: ret i64 %d
+; CHECK-NOT: ext
+; CHECK: ret
 }
 define i64 @test4(i64 %a) {
   %b = trunc i64 %a to i32
@@ -46,8 +46,9 @@ define i64 @test4(i64 %a) {
   ret i64 %d
 ; CHECK: @test4
 ; CHECK: = and i64 %a, 8
-; CHECK: %d = xor i64 {{.*}}, 8
-; CHECK: ret i64 %d
+; CHECK: = xor i64 {{.*}}, 8
+; CHECK-NOT: ext
+; CHECK: ret
 }
 
 define i32 @test5(i32 %A) {