[llvm] [InstCombine] Fold `switch(zext/sext(X))` into `switch(X)` (PR #76988)

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,122 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt %s -passes=instcombine -S | FileCheck %s
+
+define i1 @test_switch_with_zext(i16 %a, i1 %b, i1 %c) {
+; CHECK-LABEL: define i1 @test_switch_with_zext(
+; CHECK-SAME: i16 [[A:%.*]], i1 [[B:%.*]], i1 [[C:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    switch i16 [[A]], label [[SW_DEFAULT:%.*]] [
+; CHECK-NEXT:      i16 37, label [[SW_BB:%.*]]
+; CHECK-NEXT:      i16 38, label [[SW_BB]]
+; CHECK-NEXT:      i16 39, label [[SW_BB]]
+; CHECK-NEXT:    ]
+; CHECK:       sw.bb:
+; CHECK-NEXT:    ret i1 [[B]]
+; CHECK:       sw.default:
+; CHECK-NEXT:    ret i1 [[C]]
+;
+entry:
+  %a.ext = zext i16 %a to i32
+  switch i32 %a.ext, label %sw.default [
+  i32 37, label %sw.bb
+  i32 38, label %sw.bb
+  i32 39, label %sw.bb
+  ]
+
+sw.bb:
+  ret i1 %b
+sw.default:
+  ret i1 %c
+}
+
+define i1 @test_switch_with_sext(i16 %a, i1 %b, i1 %c) {
+; CHECK-LABEL: define i1 @test_switch_with_sext(
+; CHECK-SAME: i16 [[A:%.*]], i1 [[B:%.*]], i1 [[C:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    switch i16 [[A]], label [[SW_DEFAULT:%.*]] [
+; CHECK-NEXT:      i16 37, label [[SW_BB:%.*]]
+; CHECK-NEXT:      i16 38, label [[SW_BB]]
+; CHECK-NEXT:      i16 39, label [[SW_BB]]
+; CHECK-NEXT:    ]
+; CHECK:       sw.bb:
+; CHECK-NEXT:    ret i1 [[B]]
+; CHECK:       sw.default:
+; CHECK-NEXT:    ret i1 [[C]]
+;
+entry:
+  %a.ext = sext i16 %a to i32
----------------
nikic wrote:

I'd like to see a test where the sign extension matters.

https://github.com/llvm/llvm-project/pull/76988