[LLVMbugs] [Bug 19858] New: i8 checked mul is wrong on x86

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon May 26 08:21:24 PDT 2014


            Bug ID: 19858
           Summary: i8 checked mul is wrong on x86
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: kfischer at college.harvard.edu
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Consider the following code sample:

declare {i8, i1} @llvm.umul.with.overflow.i8(i8 %a, i8 %b)
define i8 @main(i32 %argc) {
  %RHS = trunc i32 %argc to i8
  %umul = call { i8, i1 } @llvm.umul.with.overflow.i8(i8 25, i8 %RHS)
  %ex = extractvalue { i8, i1 } %umul, 1
  br i1 %ex, label %L, label %L1

L:                                                ; preds = %top
  ret i8 %RHS

L1:                                               ; preds = %top
  %umul.value = extractvalue { i8, i1 } %umul, 0
  ret i8 %umul.value

Running this with `lli test.ll` gives a return value of 1 rather than 25 (i.e.
the overflow flag was set when it shouldn't have been.

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