[llvm] [InstCombine] Canonicalize manual signed mul overflows (PR #100048)

[via llvm-commits]

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@@ -343,3 +343,37 @@ define i32 @extra_and_use_mask_too_large(i32 %x, i32 %y) {
   %retval = zext i1 %overflow to i32
   ret i32 %retval
 }
+
+define i32 @smul(i32 %a, i32 %b) {
+; CHECK-LABEL: @smul(
+; CHECK-NEXT:    [[SMUL:%.*]] = call { i32, i1 } @llvm.smul.with.overflow.i32(i32 [[B:%.*]], i32 [[A:%.*]])
+; CHECK-NEXT:    [[TMP1:%.*]] = extractvalue { i32, i1 } [[SMUL]], 1
+; CHECK-NEXT:    [[CONV3:%.*]] = zext i1 [[TMP1]] to i32
+; CHECK-NEXT:    ret i32 [[CONV3]]
+;
+  %conv = sext i32 %a to i64
+  %conv1 = sext i32 %b to i64
+  %mul = mul nsw i64 %conv1, %conv
+  %1 = add nsw i64 %mul, -2147483648
+  %2 = icmp ult i64 %1, -4294967296
+  %conv3 = zext i1 %2 to i32
+  ret i32 %conv3
+}
+
+define i32 @smul2(i32 %a, i32 %b) {
+; CHECK-LABEL: @smul2(
+; CHECK-NEXT:    [[SMUL:%.*]] = call { i32, i1 } @llvm.smul.with.overflow.i32(i32 [[B:%.*]], i32 [[A:%.*]])
+; CHECK-NEXT:    [[TMP1:%.*]] = extractvalue { i32, i1 } [[SMUL]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = xor i1 [[TMP1]], true
+; CHECK-NEXT:    [[CONV3:%.*]] = zext i1 [[TMP2]] to i32
+; CHECK-NEXT:    ret i32 [[CONV3]]
+;
+  %conv = sext i32 %a to i64
+  %conv1 = sext i32 %b to i64
+  %mul = mul nsw i64 %conv1, %conv
+  %cmp = icmp sle i64 %mul, 2147483647
+  %cmp2 = icmp sge i64 %mul, -2147483648
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goldsteinn wrote:

This will get transformed to the `ult` case:
https://godbolt.org/z/Ps6Kxqjjo

https://github.com/llvm/llvm-project/pull/100048