AMDGPU: Don't fix emergency stack slot at offset 0

This forced the caller to be aware of this, which is an ugly ABI
feature.

Partially reverts r295877. The original reasons for doing this are
mostly fixed. Alloca is now in a non-0 address space, so it should be
OK to have 0 as a valid pointer. Since we treat the absolute address
as the pointer value, this part only really needed to apply to
kernels.

Since r357093, we avoid the need to increment/decrement the offset
register in more cases, and since r354816 the scavenger can fail
without spilling, so it's less critical that we try to avoid an offset
that fits in the MUBUF offset.

Restrict to callable functions for now to split this into 2 steps to
limit thte number of test updates and in case anything breaks.

llvm-svn: 362665

1 files changed, 0 insertions, 10 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index 8a08bc463da..f5fcb7cdfe0 100644
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -1940,12 +1940,6 @@ SDValue SITargetLowering::LowerFormalArguments(
   bool IsKernel = AMDGPU::isKernel(CallConv);
   bool IsEntryFunc = AMDGPU::isEntryFunctionCC(CallConv);
 
-  if (!IsEntryFunc) {
-    // 4 bytes are reserved at offset 0 for the emergency stack slot. Skip over
-    // this when allocating argument fixed offsets.
-    CCInfo.AllocateStack(4, 4);
-  }
-
   if (IsShader) {
     processShaderInputArgs(Splits, CallConv, Ins, Skipped, FType, Info);
 
@@ -2551,7 +2545,6 @@ SDValue SITargetLowering::LowerCall(CallLoweringInfo &CLI,
                           "unsupported call from graphics shader of function ");
   }
 
-  // The first 4 bytes are reserved for the callee's emergency stack slot.
   if (IsTailCall) {
     IsTailCall = isEligibleForTailCallOptimization(
       Callee, CallConv, IsVarArg, Outs, OutVals, Ins, DAG);
@@ -2578,9 +2571,6 @@ SDValue SITargetLowering::LowerCall(CallLoweringInfo &CLI,
   CCState CCInfo(CallConv, IsVarArg, MF, ArgLocs, *DAG.getContext());
   CCAssignFn *AssignFn = CCAssignFnForCall(CallConv, IsVarArg);
 
-  // The first 4 bytes are reserved for the callee's emergency stack slot.
-  CCInfo.AllocateStack(4, 4);
-
   CCInfo.AnalyzeCallOperands(Outs, AssignFn);
 
   // Get a count of how many bytes are to be pushed on the stack.