[llvm] InstSimplify: lookthru casts, binops in folding shuffles (PR #92668)

[David Green via llvm-commits]

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@@ -284,3 +284,222 @@ define <2 x i8> @splat_inserted_constant_not_canonical(<3 x i8> %x, <3 x i8> %y)
   %splat2 = shufflevector <3 x i8> %y, <3 x i8> %ins2, <2 x i32> <i32 undef, i32 5>
   ret <2 x i8> %splat2
 }
+
+define <4 x i32> @fold_identity(<4 x i32> %x) {
+; CHECK-LABEL: @fold_identity(
+; CHECK-NEXT:    ret <4 x i32> [[X:%.*]]
+;
+  %shuf = shufflevector <4 x i32> %x, <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
+  %revshuf = shufflevector <4 x i32> %shuf, <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
+  ret <4 x i32> %revshuf
+}
+
+define <4 x i32> @fold_identity2(<4 x i32> %x) {
+; CHECK-LABEL: @fold_identity2(
+; CHECK-NEXT:    [[SHL:%.*]] = shl <4 x i32> [[X:%.*]], <i32 1, i32 1, i32 1, i32 1>
+; CHECK-NEXT:    ret <4 x i32> [[SHL]]
+;
+  %shl = shl <4 x i32> %x, <i32 1, i32 1, i32 1, i32 1>
+  %shuf = shufflevector <4 x i32> %shl, <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
+  %revshuf = shufflevector <4 x i32> %shuf, <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
+  ret <4 x i32> %revshuf
+}
+
+define <4 x i32> @fold_identity3(<4 x i32> %x) {
+; CHECK-LABEL: @fold_identity3(
+; CHECK-NEXT:    [[SHL:%.*]] = shl <4 x i32> [[X:%.*]], [[X]]
+; CHECK-NEXT:    ret <4 x i32> [[SHL]]
+;
+  %shl = shl <4 x i32> %x, %x
+  %shuf = shufflevector <4 x i32> %shl, <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
+  %revshuf = shufflevector <4 x i32> %shuf, <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
+  ret <4 x i32> %revshuf
+}
+
+define <4 x i32> @not_fold_identity(<4 x i32> %x) {
+; CHECK-LABEL: @not_fold_identity(
+; CHECK-NEXT:    [[SHUF:%.*]] = shufflevector <4 x i32> [[X:%.*]], <4 x i32> poison, <4 x i32> <i32 2, i32 3, i32 0, i32 1>
+; CHECK-NEXT:    [[REVSHUF:%.*]] = shufflevector <4 x i32> [[SHUF]], <4 x i32> poison, <4 x i32> <i32 1, i32 0, i32 3, i32 2>
+; CHECK-NEXT:    ret <4 x i32> [[REVSHUF]]
+;
+  %shuf = shufflevector <4 x i32> %x, <4 x i32> poison, <4 x i32> <i32 2, i32 3, i32 0, i32 1>
+  %revshuf = shufflevector <4 x i32> %shuf, <4 x i32> poison, <4 x i32> <i32 1, i32 0, i32 3, i32 2>
+  ret <4 x i32> %revshuf
+}
+
+define <4 x i32> @not_fold_identity2(<4 x i32> %x) {
+; CHECK-LABEL: @not_fold_identity2(
+; CHECK-NEXT:    [[SHUF:%.*]] = shufflevector <4 x i32> [[X:%.*]], <4 x i32> poison, <4 x i32> <i32 2, i32 3, i32 1, i32 0>
+; CHECK-NEXT:    [[REVSHUF:%.*]] = shufflevector <4 x i32> [[SHUF]], <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
+; CHECK-NEXT:    ret <4 x i32> [[REVSHUF]]
+;
+  %shuf = shufflevector <4 x i32> %x, <4 x i32> poison, <4 x i32> <i32 2, i32 3, i32 1, i32 0>
+  %revshuf = shufflevector <4 x i32> %shuf, <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
+  ret <4 x i32> %revshuf
+}
+
+define <4 x i64> @fold_lookthrough_cast(<4 x i32> %x) {
+; CHECK-LABEL: @fold_lookthrough_cast(
+; CHECK-NEXT:    [[SHUF:%.*]] = shufflevector <4 x i32> [[X:%.*]], <4 x i32> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
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davemgreen wrote:

Would this need to remove the shuffle too?

https://github.com/llvm/llvm-project/pull/92668