[InstCombine] fold bitcasts around an extractelement (3rd try)

This is a redo of r255137 (reverted at r255227) which was a redo of 
r255124 (reverted at r255126) with a fixed check for a scalar source 
type and an added test for the failure that caused the revert.

Original commit message:

Example:
  bitcast (extractelement (bitcast <2 x float> %X to <2 x i32>), 1) to float
    --->
  extractelement <2 x float> %X, i32 1

This is part of fixing PR25543:
https://llvm.org/bugs/show_bug.cgi?id=25543

The next step will be to generalize this fold:
trunc ( lshr ( bitcast X) ) -> extractelement (X)

Ie, I'm hoping to replace the existing transform of:
bitcast ( trunc ( lshr ( bitcast X)))
added by:
http://reviews.llvm.org/rL112232

with 2 less specific transforms to catch the case in the bug report.

Differential Revision: http://reviews.llvm.org/D14879

llvm-svn: 255261

1 files changed, 34 insertions, 8 deletions

diff --git a/llvm/test/Transforms/InstCombine/bitcast.ll b/llvm/test/Transforms/InstCombine/bitcast.ll
index 2a8194e5303..bccd19cc32e 100644
--- a/llvm/test/Transforms/InstCombine/bitcast.ll
+++ b/llvm/test/Transforms/InstCombine/bitcast.ll
@@ -64,7 +64,7 @@ define float @test3(<2 x float> %A, <2 x i64> %B) {
 ; CHECK-NEXT:  ret float %add
 }
 
-; TODO: Both bitcasts are unnecessary; change the extractelement.
+; Both bitcasts are unnecessary; change the extractelement.
 
 define float @bitcast_extelt1(<2 x float> %A) {
   %bc1 = bitcast <2 x float> %A to <2 x i32>
@@ -73,13 +73,11 @@ define float @bitcast_extelt1(<2 x float> %A) {
   ret float %bc2
 
 ; CHECK-LABEL: @bitcast_extelt1(
-; CHECK-NEXT:  %bc1 = bitcast <2 x float> %A to <2 x i32>
-; CHECK-NEXT:  %ext = extractelement <2 x i32> %bc1, i32 0
-; CHECK-NEXT:  %bc2 = bitcast i32 %ext to float
+; CHECK-NEXT:  %bc2 = extractelement <2 x float> %A, i32 0
 ; CHECK-NEXT:  ret float %bc2
 }
 
-; TODO: Second bitcast can be folded into the first.
+; Second bitcast can be folded into the first.
 
 define i64 @bitcast_extelt2(<4 x float> %A) {
   %bc1 = bitcast <4 x float> %A to <2 x double>
@@ -88,12 +86,40 @@ define i64 @bitcast_extelt2(<4 x float> %A) {
   ret i64 %bc2
 
 ; CHECK-LABEL: @bitcast_extelt2(
-; CHECK-NEXT:  %bc1 = bitcast <4 x float> %A to <2 x double>
-; CHECK-NEXT:  %ext = extractelement <2 x double> %bc1, i32 1
-; CHECK-NEXT:  %bc2 = bitcast double %ext to i64
+; CHECK-NEXT:  %bc = bitcast <4 x float> %A to <2 x i64>
+; CHECK-NEXT:  %bc2 = extractelement <2 x i64> %bc, i32 1
 ; CHECK-NEXT:  ret i64 %bc2
 }
 
+; TODO: This should return %A. 
+
+define <2 x i32> @bitcast_extelt3(<2 x i32> %A) {
+  %bc1 = bitcast <2 x i32> %A to <1 x i64>
+  %ext = extractelement <1 x i64> %bc1, i32 0
+  %bc2 = bitcast i64 %ext to <2 x i32>
+  ret <2 x i32> %bc2
+
+; CHECK-LABEL: @bitcast_extelt3(
+; CHECK-NEXT:  %bc1 = bitcast <2 x i32> %A to <1 x i64>
+; CHECK-NEXT:  %ext = extractelement <1 x i64> %bc1, i32 0
+; CHECK-NEXT:  %bc2 = bitcast i64 %ext to <2 x i32>
+; CHECK-NEXT:  ret <2 x i32> %bc2
+}
+
+; Handle the case where the input is not a vector.
+
+define double @bitcast_extelt4(i128 %A) {
+  %bc1 = bitcast i128 %A to <2 x i64>
+  %ext = extractelement <2 x i64> %bc1, i32 0
+  %bc2 = bitcast i64 %ext to double
+  ret double %bc2
+
+; CHECK-LABEL: @bitcast_extelt4(
+; CHECK-NEXT:  %bc = bitcast i128 %A to <2 x double>
+; CHECK-NEXT:  %bc2 = extractelement <2 x double> %bc, i32 0
+; CHECK-NEXT:  ret double %bc2
+}
+
 define <2 x i32> @test4(i32 %A, i32 %B){
   %tmp38 = zext i32 %A to i64
   %tmp32 = zext i32 %B to i64