[llvm] ca2e8fc - Update callers of isTriviallyReMaterializable to check trivialness (#160319)

[via llvm-commits]

Author: Philip Reames
Date: 2025-09-23T11:57:36-07:00
New Revision: ca2e8fc928ad103f46ca9f827e147c43db3a5c47

URL: https://github.com/llvm/llvm-project/commit/ca2e8fc928ad103f46ca9f827e147c43db3a5c47
DIFF: https://github.com/llvm/llvm-project/commit/ca2e8fc928ad103f46ca9f827e147c43db3a5c47.diff

LOG: Update callers of isTriviallyReMaterializable to check trivialness (#160319)

This is a preparatory change for an upcoming reorganization of our
rematerialization APIs. Despite the interface being documented as
"trivial" (meaning no virtual register uses on the instruction being
considered for remat), our actual implementation inconsistently supports
non-trivial remat, and certain backends (AMDGPU and RISC-V mostly) lie
about instructions being trivial to abuse that. We want to allow
non-triial remat more broadly, but first we need to do some cleanup to
make it understandable what's going on.

These three call sites are ones which appear to actually want the
trivial definition, and appear fairly low risk to change.

p.s. I'm deliberately *not* updating any APIs in this change, I'm going
to do that as a followup once it's clear which category each callsite
fits in.

Added: 
    

Modified: 
    llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
    llvm/lib/CodeGen/RegAllocScore.cpp
    llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 05d3d18aa9557..1db742253d594 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -2212,7 +2212,11 @@ findPrologueEndLoc(const MachineFunction *MF) {
       -> std::optional<std::pair<const MachineInstr *, bool>> {
     // Is this instruction trivial data shuffling or frame-setup?
     bool isCopy = (TII.isCopyInstr(MI) ? true : false);
-    bool isTrivRemat = TII.isTriviallyReMaterializable(MI);
+    bool isTrivRemat =
+        TII.isTriviallyReMaterializable(MI) &&
+        llvm::all_of(MI.all_uses(), [](const MachineOperand &MO) {
+          return MO.getReg().isVirtual();
+        });
     bool isFrameSetup = MI.getFlag(MachineInstr::FrameSetup);
 
     if (!isFrameSetup && MI.getDebugLoc()) {

diff  --git a/llvm/lib/CodeGen/RegAllocScore.cpp b/llvm/lib/CodeGen/RegAllocScore.cpp
index b86647dbe0a48..ce1eea3519b71 100644
--- a/llvm/lib/CodeGen/RegAllocScore.cpp
+++ b/llvm/lib/CodeGen/RegAllocScore.cpp
@@ -79,8 +79,11 @@ llvm::calculateRegAllocScore(const MachineFunction &MF,
         return MBFI.getBlockFreqRelativeToEntryBlock(&MBB);
       },
       [&](const MachineInstr &MI) {
-        return MF.getSubtarget().getInstrInfo()->isTriviallyReMaterializable(
-            MI);
+        auto *TTI = MF.getSubtarget().getInstrInfo();
+        return TTI->isTriviallyReMaterializable(MI) &&
+               llvm::all_of(MI.all_uses(), [](const MachineOperand &MO) {
+                 return MO.getReg().isVirtual();
+               });
       });
 }
 

diff  --git a/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
index 08ca20b5eef6e..7591541779884 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
@@ -260,7 +260,10 @@ static void query(const MachineInstr &MI, bool &Read, bool &Write,
 // Test whether Def is safe and profitable to rematerialize.
 static bool shouldRematerialize(const MachineInstr &Def,
                                 const WebAssemblyInstrInfo *TII) {
-  return Def.isAsCheapAsAMove() && TII->isTriviallyReMaterializable(Def);
+  return Def.isAsCheapAsAMove() && TII->isTriviallyReMaterializable(Def) &&
+         llvm::all_of(Def.all_uses(), [](const MachineOperand &MO) {
+           return MO.getReg().isVirtual();
+         });
 }
 
 // Identify the definition for this register at this point. This is a