[llvm] PreISelIntrinsicLowering: Lower llvm.log to a loop if scalable vec arg (PR #129744)

[Stephen Long via llvm-commits]

https://github.com/steplong updated https://github.com/llvm/llvm-project/pull/129744

>From 025b8af5860f4faefe6026007a0b176ed4d7b008 Mon Sep 17 00:00:00 2001
From: Stephen Long <steplong at quicinc.com>
Date: Tue, 4 Mar 2025 08:54:24 -0800
Subject: [PATCH] PreISelIntrinsicLowering: Lower llvm.log to a loop if
 scalable vec arg

Similar to ab976a1, but for llvm.log.
---
 llvm/lib/CodeGen/PreISelIntrinsicLowering.cpp |  4 +-
 llvm/lib/CodeGen/TargetLoweringBase.cpp       |  2 +
 .../AArch64/expand-log.ll                     | 43 +++++++++++++++++++
 3 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/Transforms/PreISelIntrinsicLowering/AArch64/expand-log.ll

diff --git a/llvm/lib/CodeGen/PreISelIntrinsicLowering.cpp b/llvm/lib/CodeGen/PreISelIntrinsicLowering.cpp
index 27fa0b43d74f6..2081796935e2a 100644
--- a/llvm/lib/CodeGen/PreISelIntrinsicLowering.cpp
+++ b/llvm/lib/CodeGen/PreISelIntrinsicLowering.cpp
@@ -560,13 +560,15 @@ bool PreISelIntrinsicLowering::lowerIntrinsics(Module &M) const {
       break;
     case Intrinsic::exp:
     case Intrinsic::exp2:
+    case Intrinsic::log:
       Changed |= forEachCall(F, [&](CallInst *CI) {
         Type *Ty = CI->getArgOperand(0)->getType();
         if (!isa<ScalableVectorType>(Ty))
           return false;
         const TargetLowering *TL = TM->getSubtargetImpl(F)->getTargetLowering();
         unsigned Op = TL->IntrinsicIDToISD(F.getIntrinsicID());
-        if (!TL->isOperationExpand(Op, EVT::getEVT(Ty)))
+        if (Op == ISD::DELETED_NODE ||
+            !TL->isOperationExpand(Op, EVT::getEVT(Ty)))
           return false;
         return lowerUnaryVectorIntrinsicAsLoop(M, CI);
       });
diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index f5ea3c0b47d6a..0391bb00ed2cf 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -1861,6 +1861,8 @@ int TargetLoweringBase::IntrinsicIDToISD(Intrinsic::ID ID) const {
     return ISD::FEXP;
   case Intrinsic::exp2:
     return ISD::FEXP2;
+  case Intrinsic::log:
+    return ISD::FLOG;
   default:
     return ISD::DELETED_NODE;
   }
diff --git a/llvm/test/Transforms/PreISelIntrinsicLowering/AArch64/expand-log.ll b/llvm/test/Transforms/PreISelIntrinsicLowering/AArch64/expand-log.ll
new file mode 100644
index 0000000000000..424729f498aa6
--- /dev/null
+++ b/llvm/test/Transforms/PreISelIntrinsicLowering/AArch64/expand-log.ll
@@ -0,0 +1,43 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=pre-isel-intrinsic-lowering -S < %s | FileCheck %s
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32"
+target triple = "aarch64"
+
+define <vscale x 4 x float> @scalable_vec_log(<vscale x 4 x float> %input) {
+; CHECK-LABEL: define <vscale x 4 x float> @scalable_vec_log(
+; CHECK-SAME: <vscale x 4 x float> [[INPUT:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[TMP2:%.*]] = mul i64 [[TMP1]], 4
+; CHECK-NEXT:    br label %[[BB3:.*]]
+; CHECK:       [[BB3]]:
+; CHECK-NEXT:    [[TMP4:%.*]] = phi i64 [ 0, [[TMP0:%.*]] ], [ [[TMP9:%.*]], %[[BB3]] ]
+; CHECK-NEXT:    [[TMP5:%.*]] = phi <vscale x 4 x float> [ [[INPUT]], [[TMP0]] ], [ [[TMP8:%.*]], %[[BB3]] ]
+; CHECK-NEXT:    [[TMP6:%.*]] = extractelement <vscale x 4 x float> [[TMP5]], i64 [[TMP4]]
+; CHECK-NEXT:    [[TMP7:%.*]] = call float @llvm.log.f32(float [[TMP6]])
+; CHECK-NEXT:    [[TMP8]] = insertelement <vscale x 4 x float> [[TMP5]], float [[TMP7]], i64 [[TMP4]]
+; CHECK-NEXT:    [[TMP9]] = add i64 [[TMP4]], 1
+; CHECK-NEXT:    [[TMP10:%.*]] = icmp eq i64 [[TMP9]], [[TMP2]]
+; CHECK-NEXT:    br i1 [[TMP10]], label %[[BB11:.*]], label %[[BB3]]
+; CHECK:       [[BB11]]:
+; CHECK-NEXT:    ret <vscale x 4 x float> [[TMP8]]
+;
+  %output = call <vscale x 4 x float> @llvm.log.nxv4f32(<vscale x 4 x float> %input)
+  ret <vscale x 4 x float> %output
+}
+
+define <4 x float> @fixed_vec_log(<4 x float> %input) {
+; CHECK-LABEL: define <4 x float> @fixed_vec_log(
+; CHECK-SAME: <4 x float> [[INPUT:%.*]]) {
+; CHECK-NEXT:    [[OUTPUT:%.*]] = call <4 x float> @llvm.log.v4f32(<4 x float> [[INPUT]])
+; CHECK-NEXT:    ret <4 x float> [[OUTPUT]]
+;
+  %output = call <4 x float> @llvm.log.v4f32(<4 x float> %input)
+  ret <4 x float> %output
+}
+
+declare <4 x float> @llvm.log.v4f32(<4 x float>) #0
+declare <vscale x 4 x float> @llvm.log.nxv4f32(<vscale x 4 x float>) #0
+
+; CHECK: attributes #0 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
+; CHECK-NEXT: attributes #1 = { nocallback nofree nosync nounwind willreturn memory(none) }
+attributes #0 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }