[InstCombine] change bitwise logic type to eliminate bitcasts

In PR27925:
https://llvm.org/bugs/show_bug.cgi?id=27925

...we proposed adding this fold to eliminate a bitcast. In D20774, there was 
some concern about changing the type of a bitwise op as well as creating 
bitcasts that might not be free for a target. However, if we're strictly 
eliminating an instruction (by limiting this to one-use ops), then we should 
be able to do this in InstCombine.

But we're cautiously restricting the transform for now to vector types to
avoid possible backend problems. A transform to make sure the logic op is
legal for the target should be added to reverse this transform and improve
codegen.

Differential Revision: https://reviews.llvm.org/D26641

llvm-svn: 287707

1 files changed, 25 insertions, 4 deletions

diff --git a/llvm/test/Transforms/InstCombine/bitcast.ll b/llvm/test/Transforms/InstCombine/bitcast.ll
index 8d8c25a1095..49cb5618831 100644
--- a/llvm/test/Transforms/InstCombine/bitcast.ll
+++ b/llvm/test/Transforms/InstCombine/bitcast.ll
@@ -74,10 +74,8 @@ define <2 x i32> @or_bitcast_int_to_vec(i64 %a) {
 
 define <4 x i32> @bitcasts_and_bitcast(<4 x i32> %a, <8 x i16> %b) {
 ; CHECK-LABEL: @bitcasts_and_bitcast(
-; CHECK-NEXT:    [[BC1:%.*]] = bitcast <4 x i32> %a to <2 x i64>
-; CHECK-NEXT:    [[BC2:%.*]] = bitcast <8 x i16> %b to <2 x i64>
-; CHECK-NEXT:    [[AND:%.*]] = and <2 x i64> [[BC2]], [[BC1]]
-; CHECK-NEXT:    [[BC3:%.*]] = bitcast <2 x i64> [[AND]] to <4 x i32>
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast <8 x i16> %b to <4 x i32>
+; CHECK-NEXT:    [[BC3:%.*]] = and <4 x i32> [[TMP1]], %a
 ; CHECK-NEXT:    ret <4 x i32> [[BC3]]
 ;
   %bc1 = bitcast <4 x i32> %a to <2 x i64>
@@ -87,6 +85,27 @@ define <4 x i32> @bitcasts_and_bitcast(<4 x i32> %a, <8 x i16> %b) {
   ret <4 x i32> %bc3
 }
 
+; The destination must have an integer element type.
+; FIXME: We can still eliminate one bitcast in this test by doing the logic op
+; in the type of the input that has an integer element type.
+
+define <4 x float> @bitcasts_and_bitcast_to_fp(<4 x float> %a, <8 x i16> %b) {
+; CHECK-LABEL: @bitcasts_and_bitcast_to_fp(
+; CHECK-NEXT:    [[BC1:%.*]] = bitcast <4 x float> %a to <2 x i64>
+; CHECK-NEXT:    [[BC2:%.*]] = bitcast <8 x i16> %b to <2 x i64>
+; CHECK-NEXT:    [[AND:%.*]] = and <2 x i64> [[BC2]], [[BC1]]
+; CHECK-NEXT:    [[BC3:%.*]] = bitcast <2 x i64> [[AND]] to <4 x float>
+; CHECK-NEXT:    ret <4 x float> [[BC3]]
+;
+  %bc1 = bitcast <4 x float> %a to <2 x i64>
+  %bc2 = bitcast <8 x i16> %b to <2 x i64>
+  %and = and <2 x i64> %bc2, %bc1
+  %bc3 = bitcast <2 x i64> %and to <4 x float>
+  ret <4 x float> %bc3
+}
+
+; FIXME: Transform limited from changing vector op to integer op to avoid codegen problems.
+
 define i128 @bitcast_or_bitcast(i128 %a, <2 x i64> %b) {
 ; CHECK-LABEL: @bitcast_or_bitcast(
 ; CHECK-NEXT:    [[BC1:%.*]] = bitcast i128 %a to <2 x i64>
@@ -100,6 +119,8 @@ define i128 @bitcast_or_bitcast(i128 %a, <2 x i64> %b) {
   ret i128 %bc2
 }
 
+; FIXME: Transform limited from changing integer op to vector op to avoid codegen problems.
+
 define <4 x i32> @bitcast_xor_bitcast(<4 x i32> %a, i128 %b) {
 ; CHECK-LABEL: @bitcast_xor_bitcast(
 ; CHECK-NEXT:    [[BC1:%.*]] = bitcast <4 x i32> %a to i128