[llvm] [InstCombine] Support division of numbers that can be converted to a shift (PR #88220)

[via llvm-commits]

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@@ -1638,6 +1638,30 @@ define i32 @sdiv_mul_sub_nsw(i32 %x, i32 %y) {
   ret i32 %d
 }
 
+  define i32 @mul_by_150_udiv_by_100 (i32 %0) {
+; CHECK-LABEL: @mul_by_150_udiv_by_100(
+; CHECK-NEXT:    [[TMP2:%.*]] = mul i32 [[TMP0:%.*]], 3
+; CHECK-NEXT:    [[TMP3:%.*]] = lshr i32 [[TMP2]], 1
+; CHECK-NEXT:    ret i32 [[TMP3]]
+;
+  %2 = mul nuw i32 %0, 150
+  %3 = udiv i32 %2, 100
+  ret i32 %3
+}
+
+;negative case, no nuw
+
+  define i32 @mul_by_150_sdiv_by_100 (i32 %0) {
+; CHECK-LABEL: @mul_by_150_sdiv_by_100(
+; CHECK-NEXT:    [[TMP2:%.*]] = mul nsw i32 [[TMP0:%.*]], 3
+; CHECK-NEXT:    [[TMP3:%.*]] = lshr i32 [[TMP2]], 1
+; CHECK-NEXT:    ret i32 [[TMP3]]
+;
+  %2 = mul nsw i32 %0, 150
+  %3 = sdiv i32 %2, 100
+  ret i32 %3
+}
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goldsteinn wrote:

Missing some negative tests.

https://github.com/llvm/llvm-project/pull/88220