[llvm] [SCCP] Handle llvm.vscale intrinsic calls (PR #114033)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-function-specialization

Author: Hari Limaye (hazzlim)

<details>
<summary>Changes</summary>

Teach SCCP to compute a constant range for calls to llvm.vscale intrinsics.

---
Full diff: https://github.com/llvm/llvm-project/pull/114033.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Utils/SCCPSolver.cpp (+6) 
- (added) llvm/test/Transforms/SCCP/vscale-intrinsic.ll (+56) 


``````````diff
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index c65710ea7551ac..4225e7e80fda6f 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -1923,6 +1923,12 @@ void SCCPInstVisitor::handleCallResult(CallBase &CB) {
       return (void)mergeInValue(IV, &CB, CopyOfVal);
     }
 
+    if (II->getIntrinsicID() == Intrinsic::vscale) {
+      unsigned BitWidth = CB.getType()->getScalarSizeInBits();
+      const ConstantRange Result = getVScaleRange(II->getFunction(), BitWidth);
+      return (void)mergeInValue(II, ValueLatticeElement::getRange(Result));
+    }
+
     if (ConstantRange::isIntrinsicSupported(II->getIntrinsicID())) {
       // Compute result range for intrinsics supported by ConstantRange.
       // Do this even if we don't know a range for all operands, as we may
diff --git a/llvm/test/Transforms/SCCP/vscale-intrinsic.ll b/llvm/test/Transforms/SCCP/vscale-intrinsic.ll
new file mode 100644
index 00000000000000..ca08c305c3059d
--- /dev/null
+++ b/llvm/test/Transforms/SCCP/vscale-intrinsic.ll
@@ -0,0 +1,56 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=sccp -S | FileCheck %s
+
+define i1 @vscale_i32_noattr() {
+; CHECK-LABEL: define i1 @vscale_i32_noattr() {
+; CHECK-NEXT:    [[SCALE:%.*]] = call i32 @llvm.vscale.i32()
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp ule i32 [[SCALE]], 16
+; CHECK-NEXT:    [[RES:%.*]] = and i1 true, [[CMP2]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %scale = call i32 @llvm.vscale.i32()
+  %cmp1 = icmp uge i32 %scale, 1
+  %cmp2 = icmp ule i32 %scale, 16
+  %res = and i1 %cmp1, %cmp2
+  ret i1 %res
+}
+
+define i1 @vscale_i32_attr() vscale_range(1, 16) {
+; CHECK-LABEL: define i1 @vscale_i32_attr(
+; CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    [[SCALE:%.*]] = call i32 @llvm.vscale.i32()
+; CHECK-NEXT:    ret i1 true
+;
+  %scale = call i32 @llvm.vscale.i32()
+  %cmp1 = icmp uge i32 %scale, 1
+  %cmp2 = icmp ule i32 %scale, 16
+  %res = and i1 %cmp1, %cmp2
+  ret i1 %res
+}
+
+define i1 @vscale_i64_noattr() {
+; CHECK-LABEL: define i1 @vscale_i64_noattr() {
+; CHECK-NEXT:    [[SCALE:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp ule i64 [[SCALE]], 16
+; CHECK-NEXT:    [[RES:%.*]] = and i1 true, [[CMP2]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %scale = call i64 @llvm.vscale.i64()
+  %cmp1 = icmp uge i64 %scale, 1
+  %cmp2 = icmp ule i64 %scale, 16
+  %res = and i1 %cmp1, %cmp2
+  ret i1 %res
+}
+
+define i1 @vscale_i64_attr() vscale_range(1, 16) {
+; CHECK-LABEL: define i1 @vscale_i64_attr(
+; CHECK-SAME: ) #[[ATTR0]] {
+; CHECK-NEXT:    [[SCALE:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    ret i1 true
+;
+  %scale = call i64 @llvm.vscale.i64()
+  %cmp1 = icmp uge i64 %scale, 1
+  %cmp2 = icmp ule i64 %scale, 16
+  %res = and i1 %cmp1, %cmp2
+  ret i1 %res
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/114033