Recommit r171461 which was incorrectly reverted. Mark DIV/IDIV instructions hasSideEffects=1 because they can trap when dividing by 0. This is needed to keep early if conversion from moving them across basic blocks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171608 91177308-0d34-0410-b5e6-96231b3b80d8

Author: topperc

lib/Target/X86/X86InstrArithmetic.td

@@ -266,7 +266,7 @@ def IMUL64rmi8 : RIi8<0x6B, MRMSrcMem,                      // GR64 = [mem64]*I8
 
 
 // unsigned division/remainder
-let hasSideEffects = 0 in {
+let hasSideEffects = 1 in { // so that we don't speculatively execute
 let Defs = [AL,EFLAGS,AX], Uses = [AX] in
 def DIV8r  : I<0xF6, MRM6r, (outs),  (ins GR8:$src),    // AX/r8 = AL,AH
                "div{b}\t$src", [], IIC_DIV8_REG>;

test/CodeGen/X86/early-ifcvt.ll

@@ -142,3 +142,34 @@ save_state_and_return:
 }
 
 declare void @BZ2_bz__AssertH__fail()
+
+; Make sure we don't speculate on div/idiv instructions
+; CHECK: test_idiv
+; CHECK-NOT: cmov
+define i32 @test_idiv(i32 %a, i32 %b) nounwind uwtable readnone ssp {
+  %1 = icmp eq i32 %b, 0
+  br i1 %1, label %4, label %2
+
+; <label>:2                                       ; preds = %0
+  %3 = sdiv i32 %a, %b
+  br label %4
+
+; <label>:4                                       ; preds = %0, %2
+  %5 = phi i32 [ %3, %2 ], [ %a, %0 ]
+  ret i32 %5
+}
+
+; CHECK: test_div
+; CHECK-NOT: cmov
+define i32 @test_div(i32 %a, i32 %b) nounwind uwtable readnone ssp {
+  %1 = icmp eq i32 %b, 0
+  br i1 %1, label %4, label %2
+
+; <label>:2                                       ; preds = %0
+  %3 = udiv i32 %a, %b
+  br label %4
+
+; <label>:4                                       ; preds = %0, %2
+  %5 = phi i32 [ %3, %2 ], [ %a, %0 ]
+  ret i32 %5
+}