[llvm] [SelectionDAG] Simplify vselect true, T, F -> T (PR #100992)
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Mon Jul 29 02:19:25 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-selectiondag
Author: Luke Lau (lukel97)
<details>
<summary>Changes</summary>
This addresses a TODO where we can fold a vselect to it's true operand if the boolean is known to be all trues, checking getBooleanContents.
---
Full diff: https://github.com/llvm/llvm-project/pull/100992.diff
2 Files Affected:
- (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (+17-3)
- (added) llvm/test/CodeGen/RISCV/rvv/vp-select.ll (+10)
``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index daebcdabda984..1876bf3f18c21 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -9927,13 +9927,27 @@ SDValue SelectionDAG::simplifySelect(SDValue Cond, SDValue T, SDValue F) {
if (auto *CondC = dyn_cast<ConstantSDNode>(Cond))
return CondC->isZero() ? F : T;
- // TODO: This should simplify VSELECT with non-zero constant condition using
- // something like this (but check boolean contents to be complete?):
if (ConstantSDNode *CondC = isConstOrConstSplat(Cond, /*AllowUndefs*/ false,
- /*AllowTruncation*/ true))
+ /*AllowTruncation*/ true)) {
if (CondC->isZero())
return F;
+ switch (TLI->getBooleanContents(Cond.getValueType())) {
+ case TargetLowering::UndefinedBooleanContent:
+ if (CondC->getAPIntValue()[0])
+ return T;
+ break;
+ case TargetLowering::ZeroOrOneBooleanContent:
+ if (CondC->isOne())
+ return T;
+ break;
+ case TargetLowering::ZeroOrNegativeOneBooleanContent:
+ if (CondC->isAllOnes())
+ return T;
+ break;
+ }
+ }
+
// select ?, T, T --> T
if (T == F)
return T;
diff --git a/llvm/test/CodeGen/RISCV/rvv/vp-select.ll b/llvm/test/CodeGen/RISCV/rvv/vp-select.ll
new file mode 100644
index 0000000000000..5c903791927c6
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/rvv/vp-select.ll
@@ -0,0 +1,10 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=riscv64 -mattr=+v -verify-machineinstrs | FileCheck %s
+
+define <vscale x 1 x i64> @all_ones(<vscale x 1 x i64> %true, <vscale x 1 x i64> %false, i32 %evl) {
+; CHECK-LABEL: all_ones:
+; CHECK: # %bb.0:
+; CHECK-NEXT: ret
+ %v = call <vscale x 1 x i64> @llvm.vp.select.nxv1i64(<vscale x 1 x i1> splat (i1 true), <vscale x 1 x i64> %true, <vscale x 1 x i64> %false, i32 %evl)
+ ret <vscale x 1 x i64> %v
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/100992
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