[InstCombine] Fold umax(X, C) + -C into usub.sat(X, C)
#118195
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@llvm/pr-subscribers-llvm-transforms Author: Yingwei Zheng (dtcxzyw) ChangesAlive2: https://alive2.llvm.org/ce/z/oSWe5S Full diff: https://github.com/llvm/llvm-project/pull/118195.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 6fe96935818531..63725e4ca8113e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -994,6 +994,12 @@ Instruction *InstCombinerImpl::foldAddWithConstant(BinaryOperator &Add) {
}
}
+ // umax(X, C) + -C --> usub.sat(X, C)
+ if (match(Op0, m_OneUse(m_UMax(m_Value(X), m_SpecificInt(-*C)))))
+ return replaceInstUsesWith(
+ Add, Builder.CreateBinaryIntrinsic(
+ Intrinsic::usub_sat, X, ConstantInt::get(Add.getType(), -*C)));
+
// Fold (add (zext (add X, -1)), 1) -> (zext X) if X is non-zero.
// TODO: There's a general form for any constant on the outer add.
if (C->isOne()) {
diff --git a/llvm/test/Transforms/InstCombine/saturating-add-sub.ll b/llvm/test/Transforms/InstCombine/saturating-add-sub.ll
index 9236d96f59a55b..d043f5b7ad116d 100644
--- a/llvm/test/Transforms/InstCombine/saturating-add-sub.ll
+++ b/llvm/test/Transforms/InstCombine/saturating-add-sub.ll
@@ -2316,3 +2316,39 @@ define i32 @uadd_sat_via_add_swapped_cmp_select_nonstrict(i32 %x, i32 %y) {
%r = select i1 %c, i32 %a, i32 -1
ret i32 %r
}
+
+define i8 @fold_add_umax_to_usub(i8 %a) {
+; CHECK-LABEL: @fold_add_umax_to_usub(
+; CHECK-NEXT: [[SEL:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[A:%.*]], i8 10)
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %umax = call i8 @llvm.umax.i8(i8 %a, i8 10)
+ %sel = add i8 %umax, -10
+ ret i8 %sel
+}
+
+define i8 @fold_add_umax_to_usub_incorrect_rhs(i8 %a) {
+; CHECK-LABEL: @fold_add_umax_to_usub_incorrect_rhs(
+; CHECK-NEXT: [[UMAX:%.*]] = call i8 @llvm.umax.i8(i8 [[A:%.*]], i8 10)
+; CHECK-NEXT: [[SEL:%.*]] = add i8 [[UMAX]], -11
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %umax = call i8 @llvm.umax.i8(i8 %a, i8 10)
+ %sel = add i8 %umax, -11
+ ret i8 %sel
+}
+
+define i8 @fold_add_umax_to_usub_multiuse(i8 %a) {
+; CHECK-LABEL: @fold_add_umax_to_usub_multiuse(
+; CHECK-NEXT: [[UMAX:%.*]] = call i8 @llvm.umax.i8(i8 [[A:%.*]], i8 10)
+; CHECK-NEXT: call void @usei8(i8 [[UMAX]])
+; CHECK-NEXT: [[SEL:%.*]] = add i8 [[UMAX]], -10
+; CHECK-NEXT: ret i8 [[SEL]]
+;
+ %umax = call i8 @llvm.umax.i8(i8 %a, i8 10)
+ call void @usei8(i8 %umax)
+ %sel = add i8 %umax, -10
+ ret i8 %sel
+}
+
+declare void @usei8(i8)
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This was referenced Dec 1, 2024
Collaborator
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/171/builds/11356 Here is the relevant piece of the build log for the reference |
Collaborator
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/146/builds/1733 Here is the relevant piece of the build log for the reference |
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Alive2: https://alive2.llvm.org/ce/z/oSWe5S
Closes #118155