[cfe-dev] Unnecessary code generated in LLVM IR

[Akash Banerjee via cfe-dev]

Please consider the following C code:




*#include <math.h>int main(void) {  double c = ceil(-INFINITY);
assert(isinf(INFINITY) && signbit(c));}*

The following LLVM IR is generated for the above code by clang:














*define dso_local i32 @main() #0 {entry:  %retval = alloca i32, align 4  %c
= alloca double, align 8  store i32 0, i32* %retval, align 4  %0 = call
double @llvm.ceil.f64(double 0xFFF0000000000000)  store double %0, double*
%c, align 8  br i1 true, label %cond.true, label %cond.false
  //Unnecessary conditional branchcond.true:
         ; preds = %entry  %call = call i32 @__isinff(float
0x7FF0000000000000) #4  %tobool = icmp ne i32 %call, 0  br i1 %tobool,
label %land.rhs, label %land.endcond.false:
      ; preds = %entry**    //Unnecessary Block*


*  br i1 false, label %cond.true1, label %cond.false4cond.true1:
                            ; preds = %cond.false*





















*   //Unnecessary Block  %call2 = call i32 @__isinf(double
0x7FF0000000000000) #4  %tobool3 = icmp ne i32 %call2, 0  br i1 %tobool3,
label %land.rhs, label %land.endcond.false4:
       ; preds = %cond.false   //Unnecessary Block  %call5 = call i32
@__isinfl(x86_fp80 0xK7FFF8000000000000000) #4  %tobool6 = icmp ne i32
%call5, 0  br i1 %tobool6, label %land.rhs, label %land.endland.rhs:
                                  ; preds = %cond.false4, %cond.true1,
%cond.true  %1 = load double, double* %c, align 8  %2 = bitcast double %1
to i64  %3 = icmp slt i64 %2, 0  br label %land.endland.end:
                          ; preds = %land.rhs, %cond.false4, %cond.true1,
%cond.true  %4 = phi i1 [ false, %cond.false4 ], [ false, %cond.true1 ], [
false, %cond.true ], [ %3, %land.rhs ]  %land.ext = zext i1 %4 to i32
%call7 = call i32 (i32, ...) bitcast (i32 (...)* @assert to i32 (i32,
...)*)(i32 %land.ext)  %5 = load i32, i32* %retval, align 4  ret i32 %5}*

This seems to happen because of the logical and operator in the assert, and
instead, if the assert is split into two separate asserts:
*    assert(isinf(INFINITY));*
*    assert(signbit(c));*
, then the IR generated is fine.

Thanks,
Akash.
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