[LLVMbugs] [Bug 9661] New: Missed optimization: unnecessary branching

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Fri Apr 8 11:24:13 PDT 2011


           Summary: Missed optimization: unnecessary branching
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: jmuizelaar at mozilla.com
                CC: llvmbugs at cs.uiuc.edu

This code:
float clamp_float(float a) {
        if (a > 1.0f)
                return 1.0f;
        else if (a < 0.0f)
                return 0.0f;
                return a;

compiles to:

clamp_float:                            # @clamp_float
        movss   .LCPI0_0(%rip), %xmm1
        ucomiss %xmm1, %xmm0
        ja      .LBB0_2
        pxor    %xmm1, %xmm1
        maxss   %xmm0, %xmm1
.LBB0_2:                                # %return
        movaps  %xmm1, %xmm0

It should be able to be something like:
clamp_float:                            # @clamp_float
        movss   .LCPI0_0(%rip), %xmm1
        minss   %xmm1, %xmm0
        pxor    %xmm1, %xmm1
        maxss   %xmm1, %xmm0

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