[llvm] [InstCombine] Propagate flags when folding consecutative shifts (PR #94872)

[Yingwei Zheng via llvm-commits]

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@@ -2240,4 +2240,84 @@ define i129 @shift_zext_not_nneg(i8 %arg) {
   ret i129 %shl
 }
 
+define i8 @src_shl_nsw(i8 %x) {
+; CHECK-LABEL: @src_shl_nsw(
+; CHECK-NEXT:    [[R:%.*]] = shl nsw i8 32, [[X:%.*]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %sh = shl nsw i8 1, %x
+  %r = shl nsw i8 %sh, 5
+  ret i8 %r
+}
+
+define i8 @src_shl_nsw_fail(i8 %x) {
+; CHECK-LABEL: @src_shl_nsw_fail(
+; CHECK-NEXT:    [[R:%.*]] = shl i8 32, [[X:%.*]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %sh = shl nsw i8 1, %x
+  %r = shl i8 %sh, 5
+  ret i8 %r
+}
+
+define i8 @src_shl_nuw(i8 %x) {
+; CHECK-LABEL: @src_shl_nuw(
+; CHECK-NEXT:    [[R:%.*]] = shl nuw i8 12, [[X:%.*]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %sh = shl nuw i8 3, %x
+  %r = shl nuw i8 %sh, 2
+  ret i8 %r
+}
+
+define i8 @src_shl_nuw_fail(i8 %x) {
+; CHECK-LABEL: @src_shl_nuw_fail(
+; CHECK-NEXT:    [[R:%.*]] = shl i8 12, [[X:%.*]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %sh = shl i8 3, %x
+  %r = shl nuw i8 %sh, 2
+  ret i8 %r
+}
+
+define i8 @src_lshr_exact(i8 %x) {
+; CHECK-LABEL: @src_lshr_exact(
+; CHECK-NEXT:    [[R:%.*]] = lshr exact i8 48, [[X:%.*]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %sh = lshr exact i8 96, %x
+  %r = lshr exact i8 %sh, 1
+  ret i8 %r
+}
+
+define i8 @src_lshr_exact_fail(i8 %x) {
+; CHECK-LABEL: @src_lshr_exact_fail(
+; CHECK-NEXT:    [[R:%.*]] = lshr i8 48, [[X:%.*]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %sh = lshr exact i8 96, %x
+  %r = lshr i8 %sh, 1
+  ret i8 %r
+}
+
+define i8 @src_ashr_exact(i8 %x) {
+; CHECK-LABEL: @src_ashr_exact(
+; CHECK-NEXT:    [[R:%.*]] = lshr exact i8 8, [[X:%.*]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %sh = ashr exact i8 32, %x
----------------
dtcxzyw wrote:

Can you replace LHS with a negative number?


https://github.com/llvm/llvm-project/pull/94872