PNaCl: Add ExpandConstantExpr pass for converting ConstantExprs to Instructions

test/Transforms/NaCl/expand-constantexpr.ll

+; RUN: opt < %s -expand-constant-expr -S | FileCheck %s
+
+@global_var1 = global i32 123
+@global_var2 = global i32 123
+
+
+define i8* @constantexpr_bitcast() {
+  ret i8* bitcast (i32* @global_var1 to i8*)
+}
+; CHECK: @constantexpr_bitcast()
+; CHECK: %expanded = bitcast i32* @global_var1 to i8*
+; CHECK: ret i8* %expanded
+
+
+define i32 @constantexpr_nested() {
+  ret i32 add (i32 ptrtoint (i32* @global_var1 to i32),
+               i32 ptrtoint (i32* @global_var2 to i32))
+}
+; CHECK: @constantexpr_nested
+; CHECK: %expanded1 = ptrtoint i32* @global_var1 to i32
+; CHECK: %expanded2 = ptrtoint i32* @global_var2 to i32
+; CHECK: %expanded = add i32 %expanded1, %expanded2
+; CHECK: ret i32 %expanded
+
+
+define i32 @constantexpr_phi() {
+entry:
+  br label %label
+label:
+  %result = phi i32 [ ptrtoint (i32* @global_var1 to i32), %entry ]
+  ret i32 %result
+}
+; CHECK: @constantexpr_phi
+; CHECK: entry:
+; CHECK: %expanded = ptrtoint i32* @global_var1 to i32
+; CHECK: br label %label
+; CHECK: label:
+; CHECK: %result = phi i32 [ %expanded, %entry ]
+
+
+; This tests that ExpandConstantExpr correctly handles a PHI node that
+; contains the same ConstantExpr twice.
+; Using replaceAllUsesWith() is not correct on a PHI node when the
+; new instruction has to be added to an incoming block.
+define i32 @constantexpr_phi_twice(i1 %arg) {
+entry:
+  br i1 %arg, label %iftrue, label %iffalse
+iftrue:
+  br label %exit
+iffalse:
+  br label %exit
+exit:
+  %result = phi i32 [ ptrtoint (i32* @global_var1 to i32), %iftrue ],
+                    [ ptrtoint (i32* @global_var1 to i32), %iffalse ]
+  ret i32 %result
+}
+; CHECK: @constantexpr_phi_twice
+; CHECK: iftrue:
+; CHECK: %expanded = ptrtoint i32* @global_var1 to i32
+; CHECK: iffalse:
+; CHECK: %expanded1 = ptrtoint i32* @global_var1 to i32
+; CHECK: exit: