[llvm] [SimplifyCFG] Treat umul + extract pattern as cheap single instruction. (PR #124933)

[Gábor Spaits via llvm-commits]

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@@ -0,0 +1,73 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S < %s | FileCheck %s
+
+define dso_local signext range(i16 0, 2) i16 @func2(i64 noundef %x, i64 noundef %y) local_unnamed_addr #0 {
+; CHECK-LABEL: @func2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP_NOT:%.*]] = icmp eq i64 [[Y:%.*]], 0
+; CHECK-NEXT:    [[MUL:%.*]] = tail call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[Y]], i64 [[X:%.*]])
+; CHECK-NEXT:    [[MUL_OV:%.*]] = extractvalue { i64, i1 } [[MUL]], 1
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[CMP_NOT]], i1 false, i1 [[MUL_OV]]
+; CHECK-NEXT:    [[CONV:%.*]] = zext i1 [[SPEC_SELECT]] to i16
+; CHECK-NEXT:    ret i16 [[CONV]]
+;
+entry:
+  %cmp.not = icmp eq i64 %y, 0
+  br i1 %cmp.not, label %land.end, label %land.rhs
+
+land.rhs:                                         ; preds = %entry
+  %mul = tail call { i64, i1 } @llvm.umul.with.overflow.i64(i64 %y, i64 %x)
+  %mul.ov = extractvalue { i64, i1 } %mul, 1
+  br label %land.end
+
+land.end:                                         ; preds = %land.rhs, %entry
+  %0 = phi i1 [ false, %entry ], [ %mul.ov, %land.rhs ]
+  %conv = zext i1 %0 to i16
+  ret i16 %conv
+}
+
+define dso_local signext range(i32 0, 1024) i32 @noHoist(i64 noundef %x, i64 noundef %y) local_unnamed_addr #0 {
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spaits wrote:

I have added the extra code in `entry` and in `land.end` so the `EphemeralValueTracker` won't track my instruction and we don't have to use the value produced by that extra instruction in the pattern.
Now I use the value calculated by the extra instruction, so the loop won't `continue` because of it.

https://github.com/llvm/llvm-project/pull/124933