[llvm] [PEI] Materialize registers before calling insertZeroCallUsedRegs (PR #214147)

[Lucas Chollet via llvm-commits]

https://github.com/LucasChollet updated https://github.com/llvm/llvm-project/pull/214147

>From b3ef6d09dc087eec369949cedc750267eb750eac Mon Sep 17 00:00:00 2001
From: Lucas Chollet <lucas.chollet at free.fr>
Date: Tue, 4 Aug 2026 22:24:46 +0200
Subject: [PATCH 1/2] [PEI] Materialize registers before calling
 insertZeroCallUsedRegs

As insertZeroCallUsedRegs only supports physical registers, force
the materialization of any virtual registers by calling
scavengeFrameVirtualRegs.

Virtual registers can be added during the pass by
emit{Prologue,Epilogue}. For example, RISC-V uses a virtual register to
store the size of a large alloca.
---
 llvm/lib/CodeGen/PrologEpilogInserter.cpp      |  5 +++++
 llvm/test/CodeGen/RISCV/zero-call-used-regs.ll | 17 +++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index 4cfce20465e21..20ccaedd1f5c8 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -1166,6 +1166,7 @@ void PEIImpl::calculateFrameObjectOffsets(MachineFunction &MF) {
 /// prolog and epilog code to the function.
 void PEIImpl::insertPrologEpilogCode(MachineFunction &MF) {
   const TargetFrameLowering &TFI = *MF.getSubtarget().getFrameLowering();
+  const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
 
   // Add prologue to the function...
   for (MachineBasicBlock *SaveBlock : SaveBlocks)
@@ -1175,6 +1176,10 @@ void PEIImpl::insertPrologEpilogCode(MachineFunction &MF) {
   for (MachineBasicBlock *RestoreBlock : RestoreBlocks)
     TFI.emitEpilogue(MF, *RestoreBlock);
 
+  // Force the materialization of any virtual registers as insertZeroCallRegs
+  // only handles physical registers.
+  if (TRI.requiresRegisterScavenging(MF) && FrameIndexVirtualScavenging)
+    scavengeFrameVirtualRegs(MF, *RS);
   // Zero call used registers before restoring callee-saved registers.
   insertZeroCallUsedRegs(MF);
 
diff --git a/llvm/test/CodeGen/RISCV/zero-call-used-regs.ll b/llvm/test/CodeGen/RISCV/zero-call-used-regs.ll
index 46b0cba76194b..78198b4876cd5 100644
--- a/llvm/test/CodeGen/RISCV/zero-call-used-regs.ll
+++ b/llvm/test/CodeGen/RISCV/zero-call-used-regs.ll
@@ -335,5 +335,22 @@ entry:
   ret double %mul2
 }
 
+define void @huge_stack() #0 "zero-call-used-regs"="used-gpr" {
+; CHECK-LABEL: huge_stack:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    lui a0, 10
+; CHECK-NEXT:    addi a0, a0, -944
+; CHECK-NEXT:    sub sp, sp, a0
+; CHECK-NEXT:    .cfi_def_cfa_offset 40016
+; CHECK-NEXT:    lui a0, 10
+; CHECK-NEXT:    addi a0, a0, -944
+; CHECK-NEXT:    add sp, sp, a0
+; CHECK-NEXT:    .cfi_def_cfa_offset 0
+; CHECK-NEXT:    li a0, 0
+; CHECK-NEXT:    ret
+  %1 = alloca [10000 x i32], align 4
+  ret void
+}
+
 attributes #0 = { "target-cpu"="generic" "target-features"="+m,+f,+d" }
 attributes #1 = { "target-cpu"="generic" "target-features"="+m,+zdinx" }

>From 255d3385858b485131a2eae73c54942039b1ec2e Mon Sep 17 00:00:00 2001
From: Lucas Chollet <lucas.chollet at free.fr>
Date: Wed, 26 Aug 2026 23:32:59 +0200
Subject: [PATCH 2/2] Move insertZeroCallUsedRegs call location instead

---
 llvm/lib/CodeGen/PrologEpilogInserter.cpp | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index 20ccaedd1f5c8..15ceb015e5748 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -284,6 +284,8 @@ bool PEIImpl::run(MachineFunction &MF) {
   if (TRI->requiresRegisterScavenging(MF) && FrameIndexVirtualScavenging)
     scavengeFrameVirtualRegs(MF, *RS);
 
+  insertZeroCallUsedRegs(MF);
+    
   // Warn on stack size when we exceeds the given limit.
   MachineFrameInfo &MFI = MF.getFrameInfo();
   uint64_t StackSize = MFI.getStackSize();
@@ -1166,7 +1168,6 @@ void PEIImpl::calculateFrameObjectOffsets(MachineFunction &MF) {
 /// prolog and epilog code to the function.
 void PEIImpl::insertPrologEpilogCode(MachineFunction &MF) {
   const TargetFrameLowering &TFI = *MF.getSubtarget().getFrameLowering();
-  const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
 
   // Add prologue to the function...
   for (MachineBasicBlock *SaveBlock : SaveBlocks)
@@ -1176,13 +1177,6 @@ void PEIImpl::insertPrologEpilogCode(MachineFunction &MF) {
   for (MachineBasicBlock *RestoreBlock : RestoreBlocks)
     TFI.emitEpilogue(MF, *RestoreBlock);
 
-  // Force the materialization of any virtual registers as insertZeroCallRegs
-  // only handles physical registers.
-  if (TRI.requiresRegisterScavenging(MF) && FrameIndexVirtualScavenging)
-    scavengeFrameVirtualRegs(MF, *RS);
-  // Zero call used registers before restoring callee-saved registers.
-  insertZeroCallUsedRegs(MF);
-
   for (MachineBasicBlock *SaveBlock : SaveBlocks)
     TFI.inlineStackProbe(MF, *SaveBlock);