[llvm] 188582b - [RISCV] Considering existing offset in the alignment when folding ADDIs into load/store.

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2022-07-01T11:18:40-07:00
New Revision: 188582b7e0f357bb9b137b995f773d114472a9c4

URL: https://github.com/llvm/llvm-project/commit/188582b7e0f357bb9b137b995f773d114472a9c4
DIFF: https://github.com/llvm/llvm-project/commit/188582b7e0f357bb9b137b995f773d114472a9c4.diff

LOG: [RISCV] Considering existing offset in the alignment when folding ADDIs into load/store.

getPointerAlignment and ConstantPoolSDNode::getAlign only consider
the alignment of the object. If we already have a non-zero offset
into the offset that may have reduced the alignment.

Since the base pointer will become an LUI with the old offset, we
need to be sure the new offset fits in the alignment of the address
that will be used to create the LUI immediate.

I'm not sure it is possible to have a non-zero offset in the
GlobalAddressSDNode or ConstantPoolSDNode at this point today so this
may only be a theoretical bug.

Differential Revision: https://reviews.llvm.org/D129006

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp

Removed: 
    


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diff  --git a/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp b/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
index 96d2bf572765..1d14d76446d4 100644
--- a/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
@@ -2269,7 +2269,8 @@ bool RISCVDAGToDAGISel::doPeepholeLoadStoreADDI(SDNode *N) {
     // to provide a margin of safety before off1 can overflow the 12 bits.
     // Check if off2 falls within that margin; if so off1+off2 can't overflow.
     const DataLayout &DL = CurDAG->getDataLayout();
-    Align Alignment = GA->getGlobal()->getPointerAlignment(DL);
+    Align Alignment = commonAlignment(GA->getGlobal()->getPointerAlignment(DL),
+                                      GA->getOffset());
     if (Offset2 != 0 && Alignment <= Offset2)
       return false;
     int64_t Offset1 = GA->getOffset();
@@ -2279,7 +2280,7 @@ bool RISCVDAGToDAGISel::doPeepholeLoadStoreADDI(SDNode *N) {
         CombinedOffset, GA->getTargetFlags());
   } else if (auto *CP = dyn_cast<ConstantPoolSDNode>(ImmOperand)) {
     // Ditto.
-    Align Alignment = CP->getAlign();
+    Align Alignment = commonAlignment(CP->getAlign(), CP->getOffset());
     if (Offset2 != 0 && Alignment <= Offset2)
       return false;
     int64_t Offset1 = CP->getOffset();