[llvm] 8560da2 - [PowerPC] Simplify PPCMCExpr::evaluateAsRelocatableImpl

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2025-03-15T12:45:18-07:00
New Revision: 8560da28c69de481f3ad147722577e87b902facb

URL: https://github.com/llvm/llvm-project/commit/8560da28c69de481f3ad147722577e87b902facb
DIFF: https://github.com/llvm/llvm-project/commit/8560da28c69de481f3ad147722577e87b902facb.diff

LOG: [PowerPC] Simplify PPCMCExpr::evaluateAsRelocatableImpl

The signedness of the @l result is dependent on the instruction operand
(gas behavior).
E.g. in `addis 3,3,65535 at l`, 65535 at l is signed. Unfortunately
we don't have the information.

bfef1dd694d4c646f79521fa3258bbb2398a990c (2014) checked `Fixup`,
which was unnecessary and mislead https://reviews.llvm.org/D115419
to make the code more complex.

In PPCMCExpr::evaluateAsRelocatableImpl we don't need to validate the
result. Just continue and rely on the validation in ELFObjectWriter.

Added: 
    

Modified: 
    llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCExpr.cpp

Removed: 
    


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diff  --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCExpr.cpp b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCExpr.cpp
index 5cd5a8f2cd4c9..60e88a68166b5 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCExpr.cpp
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCExpr.cpp
@@ -73,25 +73,17 @@ std::optional<int64_t> PPCMCExpr::evaluateAsInt64(int64_t Value) const {
 
 bool PPCMCExpr::evaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
                                           const MCFixup *Fixup) const {
+  if (!Asm)
+    return false;
   if (!getSubExpr()->evaluateAsRelocatable(Res, Asm, Fixup))
     return false;
 
+  // The signedness of the result is dependent on the instruction operand. E.g.
+  // in addis 3,3,65535 at l, 65535 at l is signed. In the absence of information at
+  // parse time (!Asm), disable the folding.
   std::optional<int64_t> MaybeInt = evaluateAsInt64(Res.getConstant());
   if (Res.isAbsolute() && MaybeInt) {
-    int64_t Result = *MaybeInt;
-    bool IsHalf16 = Fixup && Fixup->getTargetKind() == PPC::fixup_ppc_half16;
-    bool IsHalf16DS =
-        Fixup && Fixup->getTargetKind() == PPC::fixup_ppc_half16ds;
-    bool IsHalf16DQ =
-        Fixup && Fixup->getTargetKind() == PPC::fixup_ppc_half16dq;
-    bool IsHalf = IsHalf16 || IsHalf16DS || IsHalf16DQ;
-
-    if (!IsHalf && Result >= 0x8000)
-      return false;
-    if ((IsHalf16DS && (Result & 0x3)) || (IsHalf16DQ && (Result & 0xf)))
-      return false;
-
-    Res = MCValue::get(Result);
+    Res = MCValue::get(*MaybeInt);
   } else {
     Res = MCValue::get(Res.getSymA(), Res.getSymB(), Res.getConstant(),
                        getKind());