[llvm] 7e7860c - [X86][NFCI] Remove target-specific branch optimisation that's handled in BranchFolding

[Alex Bradbury via llvm-commits]

Author: Alex Bradbury
Date: 2022-08-10T10:35:31+01:00
New Revision: 7e7860c5d70d9da5d648e48daa4c2c2c2e3bd3b8

URL: https://github.com/llvm/llvm-project/commit/7e7860c5d70d9da5d648e48daa4c2c2c2e3bd3b8
DIFF: https://github.com/llvm/llvm-project/commit/7e7860c5d70d9da5d648e48daa4c2c2c2e3bd3b8.diff

LOG: [X86][NFCI] Remove target-specific branch optimisation that's handled in BranchFolding

This specific optimisation is handled in OptimizeBlock in BranchFolding
so is redundant. As discussed on the review thread, I've verified that
we have test coverage for that optimisation within test/CodeGen/X86 by
disabling the BranchFolding version of this transform after applying
this patch and rerunning the test suite.

Differential Revision: https://reviews.llvm.org/D129204

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86InstrInfo.cpp

Removed: 
    


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diff  --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index f0c8a49b17627..b130f897c2197 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -3100,44 +3100,6 @@ bool X86InstrInfo::AnalyzeBranchImpl(
 
     // Working from the bottom, handle the first conditional branch.
     if (Cond.empty()) {
-      MachineBasicBlock *TargetBB = I->getOperand(0).getMBB();
-      if (AllowModify && UnCondBrIter != MBB.end() &&
-          MBB.isLayoutSuccessor(TargetBB)) {
-        // If we can modify the code and it ends in something like:
-        //
-        //     jCC L1
-        //     jmp L2
-        //   L1:
-        //     ...
-        //   L2:
-        //
-        // Then we can change this to:
-        //
-        //     jnCC L2
-        //   L1:
-        //     ...
-        //   L2:
-        //
-        // Which is a bit more efficient.
-        // We conditionally jump to the fall-through block.
-        BranchCode = GetOppositeBranchCondition(BranchCode);
-        MachineBasicBlock::iterator OldInst = I;
-
-        BuildMI(MBB, UnCondBrIter, MBB.findDebugLoc(I), get(X86::JCC_1))
-          .addMBB(UnCondBrIter->getOperand(0).getMBB())
-          .addImm(BranchCode);
-        BuildMI(MBB, UnCondBrIter, MBB.findDebugLoc(I), get(X86::JMP_1))
-          .addMBB(TargetBB);
-
-        OldInst->eraseFromParent();
-        UnCondBrIter->eraseFromParent();
-
-        // Restart the analysis.
-        UnCondBrIter = MBB.end();
-        I = MBB.end();
-        continue;
-      }
-
       FBB = TBB;
       TBB = I->getOperand(0).getMBB();
       Cond.push_back(MachineOperand::CreateImm(BranchCode));