Merge pull request #1687 from fitzgen/sign-extend-immediates

cranelift: Sign extend `Imm64` immediates

cranelift/codegen/src/ir/immediates.rs

@@ -62,6 +62,21 @@ impl Imm64 {
     pub fn bits(&self) -> i64 {
         self.0
     }
+
+    /// Sign extend this immediate as if it were a signed integer of the given
+    /// power-of-two width.
+    pub fn sign_extend_from_width(&mut self, bit_width: u16) {
+        debug_assert!(bit_width.is_power_of_two());
+
+        if bit_width >= 64 {
+            return;
+        }
+
+        let bit_width = bit_width as i64;
+        let delta = 64 - bit_width;
+        let sign_extended = (self.0 << delta) >> delta;
+        *self = Imm64(sign_extended);
+    }
 }
 
 impl Into<i64> for Imm64 {

cranelift/codegen/src/ir/instructions.rs

@@ -296,6 +296,39 @@ impl InstructionData {
             }
         }
     }
+
+    #[inline]
+    pub(crate) fn sign_extend_immediates(&mut self, ctrl_typevar: Type) {
+        if ctrl_typevar.is_invalid() {
+            return;
+        }
+
+        let bit_width = ctrl_typevar.bits();
+
+        match self {
+            Self::BinaryImm {
+                opcode,
+                arg: _,
+                imm,
+            } => {
+                if matches!(opcode, Opcode::SdivImm | Opcode::SremImm) {
+                    imm.sign_extend_from_width(bit_width);
+                }
+            }
+            Self::IntCompareImm {
+                opcode,
+                arg: _,
+                cond,
+                imm,
+            } => {
+                debug_assert_eq!(*opcode, Opcode::IcmpImm);
+                if cond.unsigned() != *cond {
+                    imm.sign_extend_from_width(bit_width);
+                }
+            }
+            _ => {}
+        }
+    }
 }
 
 /// Information about branch and jump instructions.