[llvm] 16f126d - [InstCombine] Add bswap test pattern using bitreverse intrinsic

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-10-26T14:13:18Z
New Revision: 16f126df437f9ea19383c5486181c5e2797227f2

URL: https://github.com/llvm/llvm-project/commit/16f126df437f9ea19383c5486181c5e2797227f2
DIFF: https://github.com/llvm/llvm-project/commit/16f126df437f9ea19383c5486181c5e2797227f2.diff

LOG: [InstCombine] Add bswap test pattern using bitreverse intrinsic

This is mainly to help with future better bitreverse folding support but we can test it via bswap matching for now.

Added: 
    

Modified: 
    llvm/test/Transforms/InstCombine/bswap.ll

Removed: 
    


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diff  --git a/llvm/test/Transforms/InstCombine/bswap.ll b/llvm/test/Transforms/InstCombine/bswap.ll
index c0893dd23b80..ff1e329ba925 100644
--- a/llvm/test/Transforms/InstCombine/bswap.ll
+++ b/llvm/test/Transforms/InstCombine/bswap.ll
@@ -535,6 +535,28 @@ define <2 x i32> @partial_bswap_vector(<2 x i32> %x) {
 }
 declare <2 x i32> @llvm.bswap.v2i32(<2 x i32>)
 
+define i16 @partial_bitreverse(i16 %x) {
+; CHECK-LABEL: @partial_bitreverse(
+; CHECK-NEXT:    [[REV:%.*]] = call i16 @llvm.bitreverse.i16(i16 [[X:%.*]])
+; CHECK-NEXT:    [[LO:%.*]] = and i16 [[REV]], 255
+; CHECK-NEXT:    [[HI:%.*]] = and i16 [[REV]], -256
+; CHECK-NEXT:    [[REVLO:%.*]] = call i16 @llvm.bitreverse.i16(i16 [[LO]])
+; CHECK-NEXT:    [[REVHI:%.*]] = call i16 @llvm.bitreverse.i16(i16 [[HI]])
+; CHECK-NEXT:    [[OR:%.*]] = call i16 @llvm.fshl.i16(i16 [[REVHI]], i16 [[REVLO]], i16 8)
+; CHECK-NEXT:    ret i16 [[OR]]
+;
+  %rev= call i16 @llvm.bitreverse.i16(i16 %x)
+  %lo = and i16 %rev, 255
+  %hi = and i16 %rev, -256
+  %revlo = call i16 @llvm.bitreverse.i16(i16 %lo)
+  %revhi = call i16 @llvm.bitreverse.i16(i16 %hi)
+  %newlo = lshr i16 %revlo, 8
+  %newhi = shl  i16 %revhi, 8
+  %or = or i16 %newlo, %newhi
+  ret i16 %or
+}
+declare i16 @llvm.bitreverse.i16(i16)
+
 define i64 @bswap_and_mask_0(i64 %0) {
 ; CHECK-LABEL: @bswap_and_mask_0(
 ; CHECK-NEXT:    [[TMP2:%.*]] = and i64 [[TMP0:%.*]], -72057594037927681