[llvm] r283570 - AMDGPU/SI: Emit fixups for long branches

[Tom Stellard via llvm-commits]

Author: tstellar
Date: Fri Oct  7 11:01:18 2016
New Revision: 283570

URL: http://llvm.org/viewvc/llvm-project?rev=283570&view=rev
Log:
AMDGPU/SI: Emit fixups for long branches

Reviewers: arsenm

Subscribers: kzhuravl, wdng, nhaehnle, yaxunl, llvm-commits, tony-tye

Differential Revision: https://reviews.llvm.org/D25366

Modified:
    llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUAsmBackend.cpp

Modified: llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUAsmBackend.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUAsmBackend.cpp?rev=283570&r1=283569&r2=283570&view=diff
==============================================================================
--- llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUAsmBackend.cpp (original)
+++ llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUAsmBackend.cpp Fri Oct  7 11:01:18 2016
@@ -107,6 +107,24 @@ void AMDGPUAsmBackend::processFixupValue
                                          const MCFixup &Fixup, const MCFragment *DF,
                                          const MCValue &Target, uint64_t &Value,
                                          bool &IsResolved) {
+  MCValue Res;
+
+  // When we have complex expressions like: BB0_1 + (BB0_2 - 4), which are
+  // used for long branches, this function will be called with
+  // IsResolved = false and Value set to some pre-computed value.  In
+  // the example above, the value would be:
+  // (BB0_1 + (BB0_2 - 4)) - CurrentOffsetFromStartOfFunction.
+  // This is not what we want.  We just want the expression computation
+  // only.  The reason the MC layer subtracts the current offset from the
+  // expression is because the fixup is of kind FK_PCRel_4.
+  // For these scenarios, evaluateAsValue gives us the computation that we
+  // want.
+  if (!IsResolved && Fixup.getValue()->evaluateAsValue(Res, Layout) &&
+      Res.isAbsolute()) {
+    Value = Res.getConstant();
+    IsResolved = true;
+
+  }
   if (IsResolved)
     Value = adjustFixupValue(Fixup, Value, &Asm.getContext());
 }